Add second year
This commit is contained in:
@ -0,0 +1,186 @@
|
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- #[[CT230 - Database Systems I]]
|
||||
- **Previous Topic:** [[Database System Introduction]]
|
||||
- **Next Topic:** [[Introduction to SQL & DDL]]
|
||||
- **Relevant Slides:** 
|
||||
-
|
||||
- Why learn about relational DBMS?
|
||||
- 90% of industry / enterprise / business applications are still relational DBMS or relational DBMS with extensions (e.g., OO Relational).
|
||||
- The majority of industry applications require:
|
||||
- **Correctness**
|
||||
- **Completeness**
|
||||
- **Efficiency** (Complex optimisation techniques & complex indexing structures).
|
||||
- Relational DBMS provide this.
|
||||
-
|
||||
- What is the **Relational Data Model**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-13T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-13T10:38:01.856Z
|
||||
card-last-score:: 1
|
||||
- The **Relational Data Model** consists of collections of **relations** (often called *tables*) where each relation contains **tuples** (*rows*) and **attributes** (*columns*).
|
||||
- The relational data model is closely related to the file system model.
|
||||
- Relations are named.
|
||||
- What is a **relation**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-13T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-13T10:40:32.000Z
|
||||
card-last-score:: 1
|
||||
- A table.
|
||||
- What are **attributes**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-13T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-13T10:42:26.377Z
|
||||
card-last-score:: 1
|
||||
- **Attributes** are columns.
|
||||
- Columns / attributes are ^^almost always fixed^^ and do not change.
|
||||
- What are **tuples**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-17T10:44:51.675Z
|
||||
card-last-reviewed:: 2022-09-13T10:44:51.676Z
|
||||
card-last-score:: 3
|
||||
- **Tuples** are rows.
|
||||
- Rows contain the data.
|
||||
- There is a variable number of rows.
|
||||
- What is the **cardinality** of a relation? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-17T10:18:33.106Z
|
||||
card-last-reviewed:: 2022-09-13T10:18:33.106Z
|
||||
card-last-score:: 5
|
||||
- The ^^number of tuples in a relation^^ is referred to as the **cardinality** of that relation.
|
||||
-
|
||||
- ## Attributes / Columns
|
||||
- Each attribute belongs to **one** *domain* and has a single:
|
||||
- Name
|
||||
- Data Type
|
||||
- Format
|
||||
- ### Naming Columns #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-17T10:22:06.825Z
|
||||
card-last-reviewed:: 2022-09-13T10:22:06.825Z
|
||||
card-last-score:: 3
|
||||
- Case is **not** significant in SQL.
|
||||
- No spaces allowed.
|
||||
- No reserved keywords (e.g., date) allowed.
|
||||
- Choose meaningful variable names.
|
||||
- If given the names of relations and attributes, use ^^exactly^^ what you are given.
|
||||
- ### Data Types
|
||||
- You must ^^specify the **data type**^^ of all attributes (columns) defined.
|
||||
- Common data types used include:
|
||||
- **varchar(N)**, where **N** is an integer - used for strings.
|
||||
- date
|
||||
- int
|
||||
- double
|
||||
- You often must specify the size - especially for integers and strings
|
||||
- 
|
||||
- ### NULL
|
||||
- What are **null-valued attributes**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-17T10:42:34.881Z
|
||||
card-last-reviewed:: 2022-09-13T10:42:34.881Z
|
||||
card-last-score:: 3
|
||||
- **Null-valued attributes** are what occurs when the values of some attribute within a particular tuple may be unknown or may not apply to that particular tuple. A **null value** is used for these cases.
|
||||
- **NULL** is a special marker used in SQL to denote the ^^absence of a value.^^
|
||||
- In some cases, we wish to allow the possibility of a `NULL` value although they will often require extra handling (e.g., checking `if == NULL`).
|
||||
- In other cases, we want to prevent `NULL` from being entered as a value and specify `NOT NULL` as a **constraint** on data entry.
|
||||
- ### Atomic Attributes
|
||||
- What is an **atomic attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-17T10:18:39.518Z
|
||||
card-last-reviewed:: 2022-09-13T10:18:39.519Z
|
||||
card-last-score:: 5
|
||||
- An **atomic attribute** is an attribute which contains a ^^single value of the appropriate type^^, generally meaning, "no repeating values of the same type".
|
||||
- The relational model should **only** have atomic values.
|
||||
- ### Composite Attributes
|
||||
- What is a **composite attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-17T10:20:50.125Z
|
||||
card-last-reviewed:: 2022-09-13T10:20:50.125Z
|
||||
card-last-score:: 5
|
||||
- A **composite attribute** is an attribute that is composed of several atomic attributes.
|
||||
- E.g., `Name = FirstName, Middle Initial, Surname`.
|
||||
- We often want to decompose a composite attribute into atomic attributes unless there is a very good reason not to.
|
||||
- ### Multi-Valued Attributes
|
||||
- What is a **multi-valued attribute**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-13T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-13T10:27:11.256Z
|
||||
card-last-score:: 1
|
||||
- A **multi-valued attribute** is an attribute which has lower and upper bounds on the number of values for an individual entry.
|
||||
- The ^^opposite of an atomic attribute.^^
|
||||
- The relational model should **not** store multi-valued attributes.
|
||||
- Database design / redesign should be used to deal with this issue by creating more attributes (columns) or more tables.
|
||||
- ### Derived Attributes
|
||||
- What are **derived attributes**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-17T10:37:14.052Z
|
||||
card-last-reviewed:: 2022-09-13T10:37:14.052Z
|
||||
card-last-score:: 5
|
||||
- A **derived attribute** is an attribute whose value can be determined from another attribute.
|
||||
- E.g., you can derive age from birthdate.
|
||||
- It is a good idea to not directly store attribute which can be derived from other attributes.
|
||||
-
|
||||
- ## Collection of Relations
|
||||
- A Relational Data Model consists of a collection of relations (tables).
|
||||
- Tables are **cross-linked**.
|
||||
-
|
||||
- A relational database usually contains many relations (tables) rather than storing all data in one single relation.
|
||||
- What is a **Relational Schema**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-13T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-13T10:45:04.824Z
|
||||
card-last-score:: 1
|
||||
- A **relational schema**, $R$, is the ^^definition of a **table** in the database.^^ It can be denoted by listing the table name and the attributes:
|
||||
- $$R=\{A_1,A_2,...,A_n\}$$
|
||||
- where $A_i$ is an attribute.
|
||||
- E.g., with n=3, `works_on(essn, pno, hours)`.
|
||||
- ## Linking Tables
|
||||
- Two ^^extremely important concepts^^ within the relational model which allows tables to be linked & cross-referenced are:
|
||||
- **Primary Key** attributes.
|
||||
- **Foreign Key** attributes.
|
||||
-
|
||||
- ### Primary Keys
|
||||
- Fundamental concept of **Primary Keys**: #card
|
||||
- ^^All tuples (rows) in a relation must be **distinct**.^^
|
||||
- To ensure this, we must have one or more attributes / columns whose data values will ^^always be unique for each tuple^^ - these attributes are called **key attributes** and are used to identify a tuple in the relation.
|
||||
- There may be a few possibilities for the **primary key** - these are called **Candidate Keys**.
|
||||
- One candidate key is ultimately chosen as the primary key during the Design Stage.
|
||||
- What is a **Primary Key**? #card
|
||||
- A **primary key** is defined as one or more attributes per table where:
|
||||
- there can only be one such primary key per table
|
||||
- the primary key can never contain the `NULL` value
|
||||
- all values entered for the primary key must be unique (no duplicates across the rows)
|
||||
- Often, primary keys are used as indices.
|
||||
- We use the convention (in writing) that attribute which form primary keys are $\underline{underlined}$.
|
||||
-
|
||||
- ### Foreign Keys
|
||||
- What is a **Foreign Key**? #card
|
||||
- A **Foreign Key** is an attribute, or a set of attributes, within one table that matches or **links to** a **candidate key** of some other table (possibly the same table).
|
||||
- More formally:
|
||||
- Given relations $r_1$ and $r_2$, a **foreign key** of $r_2$ is an attribute (or set of attributes) in $r_2$ where that attribute is a **candidate key** in $r_1$. Relations $r_1$ and $r_2$ may be the same relations.
|
||||
- #### Foreign Key Terminology
|
||||
- The **parent**, **master**, or **referenced** table is the relation containing the candidate key(s).
|
||||
- The **child** or **referencing** table / relation is the relation containing the foreign key.
|
||||
-
|
||||
@ -0,0 +1,204 @@
|
||||
- #[[CT230 - Database Systems I]]
|
||||
- **Previous Topic:** [[Database System Introduction]]
|
||||
- **Next Topic:** [[Introduction to SQL & DDL]]
|
||||
- **Relevant Slides:** 
|
||||
-
|
||||
- Why learn about relational DBMS?
|
||||
- 90% of industry / enterprise / business applications are still relational DBMS or relational DBMS with extensions (e.g., OO Relational).
|
||||
- The majority of industry applications require:
|
||||
- **Correctness**
|
||||
- **Completeness**
|
||||
- **Efficiency** (Complex optimisation techniques & complex indexing structures).
|
||||
- Relational DBMS provide this.
|
||||
-
|
||||
- What is the **Relational Data Model**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:49:51.544Z
|
||||
card-last-score:: 1
|
||||
- The **Relational Data Model** consists of collections of **relations** (often called *tables*) where each relation contains **tuples** (*rows*) and **attributes** (*columns*).
|
||||
- The relational data model is closely related to the file system model.
|
||||
- Relations are named.
|
||||
- What is a **relation**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-18T20:03:40.980Z
|
||||
card-last-reviewed:: 2022-09-14T20:03:40.980Z
|
||||
card-last-score:: 5
|
||||
- A table.
|
||||
- What are **attributes**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:48:52.495Z
|
||||
card-last-score:: 1
|
||||
- **Attributes** are columns.
|
||||
- Columns / attributes are ^^almost always fixed^^ and do not change.
|
||||
- What are **tuples**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:28:29.960Z
|
||||
card-last-reviewed:: 2022-09-19T18:28:29.960Z
|
||||
card-last-score:: 5
|
||||
- **Tuples** are rows.
|
||||
- Rows contain the data.
|
||||
- There is a variable number of rows.
|
||||
- What is the **cardinality** of a relation? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-22T15:21:58.070Z
|
||||
card-last-reviewed:: 2022-09-18T15:21:58.070Z
|
||||
card-last-score:: 5
|
||||
- The ^^number of tuples in a relation^^ is referred to as the **cardinality** of that relation.
|
||||
-
|
||||
- ## Attributes / Columns
|
||||
- Each attribute belongs to **one** *domain* and has a single:
|
||||
- Name
|
||||
- Data Type
|
||||
- Format
|
||||
- ### Naming Columns #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:21:25.028Z
|
||||
card-last-reviewed:: 2022-09-19T18:21:25.029Z
|
||||
card-last-score:: 5
|
||||
- Case is **not** significant in SQL.
|
||||
- No spaces allowed.
|
||||
- No reserved keywords (e.g., date) allowed.
|
||||
- Choose meaningful variable names.
|
||||
- If given the names of relations and attributes, use ^^exactly^^ what you are given.
|
||||
- ### Data Types
|
||||
- You must ^^specify the **data type**^^ of all attributes (columns) defined.
|
||||
- Common data types used include:
|
||||
- **varchar(N)**, where **N** is an integer - used for strings.
|
||||
- date
|
||||
- int
|
||||
- double
|
||||
- You often must specify the size - especially for integers and strings
|
||||
- 
|
||||
- ### NULL
|
||||
- What are **null-valued attributes**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:27:27.406Z
|
||||
card-last-reviewed:: 2022-09-19T18:27:27.407Z
|
||||
card-last-score:: 5
|
||||
- **Null-valued attributes** are what occurs when the values of some attribute within a particular tuple may be unknown or may not apply to that particular tuple. A **null value** is used for these cases.
|
||||
- **NULL** is a special marker used in SQL to denote the ^^absence of a value.^^
|
||||
- In some cases, we wish to allow the possibility of a `NULL` value although they will often require extra handling (e.g., checking `if == NULL`).
|
||||
- In other cases, we want to prevent `NULL` from being entered as a value and specify `NOT NULL` as a **constraint** on data entry.
|
||||
- ### Atomic Attributes
|
||||
- What is an **atomic attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-22T15:22:04.435Z
|
||||
card-last-reviewed:: 2022-09-18T15:22:04.435Z
|
||||
card-last-score:: 5
|
||||
- An **atomic attribute** is an attribute which contains a ^^single value of the appropriate type^^, generally meaning, "no repeating values of the same type".
|
||||
- The relational model should **only** have atomic values.
|
||||
- ### Composite Attributes
|
||||
- What is a **composite attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-23T18:05:38.659Z
|
||||
card-last-reviewed:: 2022-09-19T18:05:38.659Z
|
||||
card-last-score:: 5
|
||||
- A **composite attribute** is an attribute that is composed of several atomic attributes.
|
||||
- E.g., `Name = FirstName, Middle Initial, Surname`.
|
||||
- We often want to decompose a composite attribute into atomic attributes unless there is a very good reason not to.
|
||||
- ### Multi-Valued Attributes
|
||||
- What is a **multi-valued attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-18T20:03:53.193Z
|
||||
card-last-reviewed:: 2022-09-14T20:03:53.193Z
|
||||
card-last-score:: 3
|
||||
- A **multi-valued attribute** is an attribute which has lower and upper bounds on the number of values for an individual entry.
|
||||
- The ^^opposite of an atomic attribute.^^
|
||||
- The relational model should **not** store multi-valued attributes.
|
||||
- Database design / redesign should be used to deal with this issue by creating more attributes (columns) or more tables.
|
||||
- ### Derived Attributes
|
||||
- What are **derived attributes**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-23T18:23:44.975Z
|
||||
card-last-reviewed:: 2022-09-19T18:23:44.975Z
|
||||
card-last-score:: 5
|
||||
- A **derived attribute** is an attribute whose value can be determined from another attribute.
|
||||
- E.g., you can derive age from birthdate.
|
||||
- It is a good idea to not directly store attribute which can be derived from other attributes.
|
||||
-
|
||||
- ## Collection of Relations
|
||||
- A Relational Data Model consists of a collection of relations (tables).
|
||||
- Tables are **cross-linked**.
|
||||
-
|
||||
- A relational database usually contains many relations (tables) rather than storing all data in one single relation.
|
||||
- What is a **Relational Schema**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:49:38.036Z
|
||||
card-last-score:: 1
|
||||
- A **relational schema**, $R$, is the ^^definition of a **table** in the database.^^ It can be denoted by listing the table name and the attributes:
|
||||
- $$R=\{A_1,A_2,...,A_n\}$$
|
||||
- where $A_i$ is an attribute.
|
||||
- E.g., with n=3, `works_on(essn, pno, hours)`.
|
||||
- ## Linking Tables
|
||||
- Two ^^extremely important concepts^^ within the relational model which allows tables to be linked & cross-referenced are:
|
||||
- **Primary Key** attributes.
|
||||
- **Foreign Key** attributes.
|
||||
-
|
||||
- ### Primary Keys
|
||||
- Fundamental concept of **Primary Keys**: #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:31:53.297Z
|
||||
card-last-reviewed:: 2022-09-19T18:31:53.298Z
|
||||
card-last-score:: 5
|
||||
- ^^All tuples (rows) in a relation must be **distinct**.^^
|
||||
- To ensure this, we must have one or more attributes / columns whose data values will ^^always be unique for each tuple^^ - these attributes are called **key attributes** and are used to identify a tuple in the relation.
|
||||
- There may be a few possibilities for the **primary key** - these are called **Candidate Keys**.
|
||||
- One candidate key is ultimately chosen as the primary key during the Design Stage.
|
||||
- What is a **Primary Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-09-23T18:33:57.863Z
|
||||
card-last-reviewed:: 2022-09-19T18:33:57.864Z
|
||||
card-last-score:: 3
|
||||
- A **primary key** is defined as one or more attributes per table where:
|
||||
- there can only be one such primary key per table
|
||||
- the primary key can never contain the `NULL` value
|
||||
- all values entered for the primary key must be unique (no duplicates across the rows)
|
||||
- Often, primary keys are used as indices.
|
||||
- We use the convention (in writing) that attribute which form primary keys are $\text{\underline{underlined}}$.
|
||||
-
|
||||
- ### Foreign Keys
|
||||
- What is a **Foreign Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-30T12:18:31.019Z
|
||||
card-last-reviewed:: 2022-09-26T12:18:31.019Z
|
||||
card-last-score:: 3
|
||||
- A **Foreign Key** is an attribute, or a set of attributes, within one table that matches or **links to** a **candidate key** of some other table (possibly the same table).
|
||||
- More formally:
|
||||
- Given relations $r_1$ and $r_2$, a **foreign key** of $r_2$ is an attribute (or set of attributes) in $r_2$ where that attribute is a **candidate key** in $r_1$. Relations $r_1$ and $r_2$ may be the same relations.
|
||||
- #### Foreign Key Terminology
|
||||
- The **parent**, **master**, or **referenced** table is the relation containing the candidate key(s).
|
||||
- The **child** or **referencing** table / relation is the relation containing the foreign key.
|
||||
-
|
||||
@ -0,0 +1,204 @@
|
||||
- #[[CT230 - Database Systems I]]
|
||||
- **Previous Topic:** [[Database System Introduction]]
|
||||
- **Next Topic:** [[Introduction to SQL & DDL]]
|
||||
- **Relevant Slides:** 
|
||||
-
|
||||
- Why learn about relational DBMS?
|
||||
- 90% of industry / enterprise / business applications are still relational DBMS or relational DBMS with extensions (e.g., OO Relational).
|
||||
- The majority of industry applications require:
|
||||
- **Correctness**
|
||||
- **Completeness**
|
||||
- **Efficiency** (Complex optimisation techniques & complex indexing structures).
|
||||
- Relational DBMS provide this.
|
||||
-
|
||||
- What is the **Relational Data Model**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:49:51.544Z
|
||||
card-last-score:: 1
|
||||
- The **Relational Data Model** consists of collections of **relations** (often called *tables*) where each relation contains **tuples** (*rows*) and **attributes** (*columns*).
|
||||
- The relational data model is closely related to the file system model.
|
||||
- Relations are named.
|
||||
- What is a **relation**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.6
|
||||
card-next-schedule:: 2022-09-18T20:03:40.980Z
|
||||
card-last-reviewed:: 2022-09-14T20:03:40.980Z
|
||||
card-last-score:: 5
|
||||
- A table.
|
||||
- What are **attributes**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:48:52.495Z
|
||||
card-last-score:: 1
|
||||
- **Attributes** are columns.
|
||||
- Columns / attributes are ^^almost always fixed^^ and do not change.
|
||||
- What are **tuples**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:28:29.960Z
|
||||
card-last-reviewed:: 2022-09-19T18:28:29.960Z
|
||||
card-last-score:: 5
|
||||
- **Tuples** are rows.
|
||||
- Rows contain the data.
|
||||
- There is a variable number of rows.
|
||||
- What is the **cardinality** of a relation? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-22T15:21:58.070Z
|
||||
card-last-reviewed:: 2022-09-18T15:21:58.070Z
|
||||
card-last-score:: 5
|
||||
- The ^^number of tuples in a relation^^ is referred to as the **cardinality** of that relation.
|
||||
-
|
||||
- ## Attributes / Columns
|
||||
- Each attribute belongs to **one** *domain* and has a single:
|
||||
- Name
|
||||
- Data Type
|
||||
- Format
|
||||
- ### Naming Columns #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:21:25.028Z
|
||||
card-last-reviewed:: 2022-09-19T18:21:25.029Z
|
||||
card-last-score:: 5
|
||||
- Case is **not** significant in SQL.
|
||||
- No spaces allowed.
|
||||
- No reserved keywords (e.g., date) allowed.
|
||||
- Choose meaningful variable names.
|
||||
- If given the names of relations and attributes, use ^^exactly^^ what you are given.
|
||||
- ### Data Types
|
||||
- You must ^^specify the **data type**^^ of all attributes (columns) defined.
|
||||
- Common data types used include:
|
||||
- **varchar(N)**, where **N** is an integer - used for strings.
|
||||
- date
|
||||
- int
|
||||
- double
|
||||
- You often must specify the size - especially for integers and strings
|
||||
- 
|
||||
- ### NULL
|
||||
- What are **null-valued attributes**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:27:27.406Z
|
||||
card-last-reviewed:: 2022-09-19T18:27:27.407Z
|
||||
card-last-score:: 5
|
||||
- **Null-valued attributes** are what occurs when the values of some attribute within a particular tuple may be unknown or may not apply to that particular tuple. A **null value** is used for these cases.
|
||||
- **NULL** is a special marker used in SQL to denote the ^^absence of a value.^^
|
||||
- In some cases, we wish to allow the possibility of a `NULL` value although they will often require extra handling (e.g., checking `if == NULL`).
|
||||
- In other cases, we want to prevent `NULL` from being entered as a value and specify `NOT NULL` as a **constraint** on data entry.
|
||||
- ### Atomic Attributes
|
||||
- What is an **atomic attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-22T15:22:04.435Z
|
||||
card-last-reviewed:: 2022-09-18T15:22:04.435Z
|
||||
card-last-score:: 5
|
||||
- An **atomic attribute** is an attribute which contains a ^^single value of the appropriate type^^, generally meaning, "no repeating values of the same type".
|
||||
- The relational model should **only** have atomic values.
|
||||
- ### Composite Attributes
|
||||
- What is a **composite attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-23T18:05:38.659Z
|
||||
card-last-reviewed:: 2022-09-19T18:05:38.659Z
|
||||
card-last-score:: 5
|
||||
- A **composite attribute** is an attribute that is composed of several atomic attributes.
|
||||
- E.g., `Name = FirstName, Middle Initial, Surname`.
|
||||
- We often want to decompose a composite attribute into atomic attributes unless there is a very good reason not to.
|
||||
- ### Multi-Valued Attributes
|
||||
- What is a **multi-valued attribute**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.36
|
||||
card-next-schedule:: 2022-09-18T20:03:53.193Z
|
||||
card-last-reviewed:: 2022-09-14T20:03:53.193Z
|
||||
card-last-score:: 3
|
||||
- A **multi-valued attribute** is an attribute which has lower and upper bounds on the number of values for an individual entry.
|
||||
- The ^^opposite of an atomic attribute.^^
|
||||
- The relational model should **not** store multi-valued attributes.
|
||||
- Database design / redesign should be used to deal with this issue by creating more attributes (columns) or more tables.
|
||||
- ### Derived Attributes
|
||||
- What are **derived attributes**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-09-23T18:23:44.975Z
|
||||
card-last-reviewed:: 2022-09-19T18:23:44.975Z
|
||||
card-last-score:: 5
|
||||
- A **derived attribute** is an attribute whose value can be determined from another attribute.
|
||||
- E.g., you can derive age from birthdate.
|
||||
- It is a good idea to not directly store attribute which can be derived from other attributes.
|
||||
-
|
||||
- ## Collection of Relations
|
||||
- A Relational Data Model consists of a collection of relations (tables).
|
||||
- Tables are **cross-linked**.
|
||||
-
|
||||
- A relational database usually contains many relations (tables) rather than storing all data in one single relation.
|
||||
- What is a **Relational Schema**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.5
|
||||
card-next-schedule:: 2022-09-18T23:00:00.000Z
|
||||
card-last-reviewed:: 2022-09-18T14:49:38.036Z
|
||||
card-last-score:: 1
|
||||
- A **relational schema**, $R$, is the ^^definition of a **table** in the database.^^ It can be denoted by listing the table name and the attributes:
|
||||
- $$R=\{A_1,A_2,...,A_n\}$$
|
||||
- where $A_i$ is an attribute.
|
||||
- E.g., with n=3, `works_on(essn, pno, hours)`.
|
||||
- ## Linking Tables
|
||||
- Two ^^extremely important concepts^^ within the relational model which allows tables to be linked & cross-referenced are:
|
||||
- **Primary Key** attributes.
|
||||
- **Foreign Key** attributes.
|
||||
-
|
||||
- ### Primary Keys
|
||||
- Fundamental concept of **Primary Keys**: #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-23T18:31:53.297Z
|
||||
card-last-reviewed:: 2022-09-19T18:31:53.298Z
|
||||
card-last-score:: 5
|
||||
- ^^All tuples (rows) in a relation must be **distinct**.^^
|
||||
- To ensure this, we must have one or more attributes / columns whose data values will ^^always be unique for each tuple^^ - these attributes are called **key attributes** and are used to identify a tuple in the relation.
|
||||
- There may be a few possibilities for the **primary key** - these are called **Candidate Keys**.
|
||||
- One candidate key is ultimately chosen as the primary key during the Design Stage.
|
||||
- What is a **Primary Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.22
|
||||
card-next-schedule:: 2022-09-23T18:33:57.863Z
|
||||
card-last-reviewed:: 2022-09-19T18:33:57.864Z
|
||||
card-last-score:: 3
|
||||
- A **primary key** is defined as one or more attributes per table where:
|
||||
- there can only be one such primary key per table
|
||||
- the primary key can never contain the `NULL` value
|
||||
- all values entered for the primary key must be unique (no duplicates across the rows)
|
||||
- Often, primary keys are used as indices.
|
||||
- We use the convention (in writing) that attribute which form primary keys are $\text{\underline{underlined}}$.
|
||||
-
|
||||
- ### Foreign Keys
|
||||
- What is a **Foreign Key**? #card
|
||||
card-last-interval:: 4
|
||||
card-repeats:: 2
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-09-30T12:18:31.019Z
|
||||
card-last-reviewed:: 2022-09-26T12:18:31.019Z
|
||||
card-last-score:: 3
|
||||
- A **Foreign Key** is an attribute, or a set of attributes, within one table that matches or **links to** a **candidate key** of some other table (possibly the same table).
|
||||
- More formally:
|
||||
- Given relations $r_1$ and $r_2$, a **foreign key** of $r_2$ is an attribute (or set of attributes) in $r_2$ where that attribute is a **candidate key** in $r_1$. Relations $r_1$ and $r_2$ may be the same relations.
|
||||
- #### Foreign Key Terminology
|
||||
- The **parent**, **master**, or **referenced** table is the relation containing the candidate key(s).
|
||||
- The **child** or **referencing** table / relation is the relation containing the foreign key.
|
||||
-
|
||||
@ -0,0 +1,204 @@
|
||||
- #[[CT230 - Database Systems I]]
|
||||
- **Previous Topic:** [[Database System Introduction]]
|
||||
- **Next Topic:** [[Introduction to SQL & DDL]]
|
||||
- **Relevant Slides:** 
|
||||
-
|
||||
- Why learn about relational DBMS?
|
||||
- 90% of industry / enterprise / business applications are still relational DBMS or relational DBMS with extensions (e.g., OO Relational).
|
||||
- The majority of industry applications require:
|
||||
- **Correctness**
|
||||
- **Completeness**
|
||||
- **Efficiency** (Complex optimisation techniques & complex indexing structures).
|
||||
- Relational DBMS provide this.
|
||||
-
|
||||
- What is the **Relational Data Model**? #card
|
||||
card-last-interval:: 10.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-10-16T13:42:39.339Z
|
||||
card-last-reviewed:: 2022-10-06T09:42:39.340Z
|
||||
card-last-score:: 5
|
||||
- The **Relational Data Model** consists of collections of **relations** (often called *tables*) where each relation contains **tuples** (*rows*) and **attributes** (*columns*).
|
||||
- The relational data model is closely related to the file system model.
|
||||
- Relations are named.
|
||||
- What is a **relation**? #card
|
||||
card-last-interval:: 11.96
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.7
|
||||
card-next-schedule:: 2022-10-12T07:45:56.825Z
|
||||
card-last-reviewed:: 2022-09-30T08:45:56.825Z
|
||||
card-last-score:: 5
|
||||
- A table.
|
||||
- What are **attributes**? #card
|
||||
card-last-interval:: 31.36
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-11-07T18:22:42.375Z
|
||||
card-last-reviewed:: 2022-10-07T10:22:42.376Z
|
||||
card-last-score:: 5
|
||||
- **Attributes** are columns.
|
||||
- Columns / attributes are ^^almost always fixed^^ and do not change.
|
||||
- What are **tuples**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-13T19:30:41.906Z
|
||||
card-last-reviewed:: 2022-10-03T14:30:41.907Z
|
||||
card-last-score:: 5
|
||||
- **Tuples** are rows.
|
||||
- Rows contain the data.
|
||||
- There is a variable number of rows.
|
||||
- What is the **cardinality** of a relation? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-14T15:39:55.046Z
|
||||
card-last-reviewed:: 2022-10-03T11:39:55.046Z
|
||||
card-last-score:: 5
|
||||
- The ^^number of tuples in a relation^^ is referred to as the **cardinality** of that relation.
|
||||
-
|
||||
- ## Attributes / Columns
|
||||
- Each attribute belongs to **one** *domain* and has a single:
|
||||
- Name
|
||||
- Data Type
|
||||
- Format
|
||||
- ### Naming Columns #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-10T17:12:54.411Z
|
||||
card-last-reviewed:: 2022-09-30T12:12:54.411Z
|
||||
card-last-score:: 5
|
||||
- Case is **not** significant in SQL.
|
||||
- No spaces allowed.
|
||||
- No reserved keywords (e.g., date) allowed.
|
||||
- Choose meaningful variable names.
|
||||
- If given the names of relations and attributes, use ^^exactly^^ what you are given.
|
||||
- ### Data Types
|
||||
- You must ^^specify the **data type**^^ of all attributes (columns) defined.
|
||||
- Common data types used include:
|
||||
- **varchar(N)**, where **N** is an integer - used for strings.
|
||||
- date
|
||||
- int
|
||||
- double
|
||||
- You often must specify the size - especially for integers and strings
|
||||
- 
|
||||
- ### NULL
|
||||
- What are **null-valued attributes**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-13T19:29:38.227Z
|
||||
card-last-reviewed:: 2022-10-03T14:29:38.227Z
|
||||
card-last-score:: 5
|
||||
- **Null-valued attributes** are what occurs when the values of some attribute within a particular tuple may be unknown or may not apply to that particular tuple. A **null value** is used for these cases.
|
||||
- **NULL** is a special marker used in SQL to denote the ^^absence of a value.^^
|
||||
- In some cases, we wish to allow the possibility of a `NULL` value although they will often require extra handling (e.g., checking `if == NULL`).
|
||||
- In other cases, we want to prevent `NULL` from being entered as a value and specify `NOT NULL` as a **constraint** on data entry.
|
||||
- ### Atomic Attributes
|
||||
- What is an **atomic attribute**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-14T15:39:57.801Z
|
||||
card-last-reviewed:: 2022-10-03T11:39:57.802Z
|
||||
card-last-score:: 5
|
||||
- An **atomic attribute** is an attribute which contains a ^^single value of the appropriate type^^, generally meaning, "no repeating values of the same type".
|
||||
- The relational model should **only** have atomic values.
|
||||
- ### Composite Attributes
|
||||
- What is a **composite attribute**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-14T15:43:20.000Z
|
||||
card-last-reviewed:: 2022-10-03T11:43:20.001Z
|
||||
card-last-score:: 5
|
||||
- A **composite attribute** is an attribute that is composed of several atomic attributes.
|
||||
- E.g., `Name = FirstName, Middle Initial, Surname`.
|
||||
- We often want to decompose a composite attribute into atomic attributes unless there is a very good reason not to.
|
||||
- ### Multi-Valued Attributes
|
||||
- What is a **multi-valued attribute**? #card
|
||||
card-last-interval:: 10.92
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-10-11T06:46:07.658Z
|
||||
card-last-reviewed:: 2022-09-30T08:46:07.658Z
|
||||
card-last-score:: 5
|
||||
- A **multi-valued attribute** is an attribute which has lower and upper bounds on the number of values for an individual entry.
|
||||
- The ^^opposite of an atomic attribute.^^
|
||||
- The relational model should **not** store multi-valued attributes.
|
||||
- Database design / redesign should be used to deal with this issue by creating more attributes (columns) or more tables.
|
||||
- ### Derived Attributes
|
||||
- What are **derived attributes**? #card
|
||||
card-last-interval:: 11.2
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-10-14T18:27:17.519Z
|
||||
card-last-reviewed:: 2022-10-03T14:27:17.520Z
|
||||
card-last-score:: 5
|
||||
- A **derived attribute** is an attribute whose value can be determined from another attribute.
|
||||
- E.g., you can derive age from birthdate.
|
||||
- It is a good idea to not directly store attribute which can be derived from other attributes.
|
||||
-
|
||||
- ## Collection of Relations
|
||||
- A Relational Data Model consists of a collection of relations (tables).
|
||||
- Tables are **cross-linked**.
|
||||
-
|
||||
- A relational database usually contains many relations (tables) rather than storing all data in one single relation.
|
||||
- What is a **Relational Schema**? #card
|
||||
card-last-interval:: 8.35
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-10-17T16:51:22.982Z
|
||||
card-last-reviewed:: 2022-10-09T08:51:22.982Z
|
||||
card-last-score:: 5
|
||||
- A **relational schema**, $R$, is the ^^definition of a **table** in the database.^^ It can be denoted by listing the table name and the attributes:
|
||||
- $$R=\{A_1,A_2,...,A_n\}$$
|
||||
- where $A_i$ is an attribute.
|
||||
- E.g., with $n=3$, `works_on(essn, pno, hours)`.
|
||||
- ## Linking Tables
|
||||
- Two ^^extremely important concepts^^ within the relational model which allows tables to be linked & cross-referenced are:
|
||||
- **Primary Key** attributes.
|
||||
- **Foreign Key** attributes.
|
||||
-
|
||||
- ### Primary Keys
|
||||
- Fundamental concept of **Primary Keys**: #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-10T17:12:29.217Z
|
||||
card-last-reviewed:: 2022-09-30T12:12:29.218Z
|
||||
card-last-score:: 5
|
||||
- ^^All tuples (rows) in a relation must be **distinct**.^^
|
||||
- To ensure this, we must have one or more attributes / columns whose data values will ^^always be unique for each tuple^^ - these attributes are called **key attributes** and are used to identify a tuple in the relation.
|
||||
- There may be a few possibilities for the **primary key** - these are called **Candidate Keys**.
|
||||
- One candidate key is ultimately chosen as the primary key during the Design Stage.
|
||||
- What is a **Primary Key**? #card
|
||||
card-last-interval:: 9.28
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-10-12T20:30:50.694Z
|
||||
card-last-reviewed:: 2022-10-03T14:30:50.694Z
|
||||
card-last-score:: 5
|
||||
- A **primary key** is defined as one or more attributes per table where:
|
||||
- there can only be one such primary key per table
|
||||
- the primary key can never contain the `NULL` value
|
||||
- all values entered for the primary key must be unique (no duplicates across the rows)
|
||||
- Often, primary keys are used as indices.
|
||||
- We use the convention (in writing) that attribute which form primary keys are $\text{\underline{underlined}}$.
|
||||
-
|
||||
- ### Foreign Keys
|
||||
- What is a **Foreign Key**? #card
|
||||
card-last-interval:: 10.24
|
||||
card-repeats:: 3
|
||||
card-ease-factor:: 2.56
|
||||
card-next-schedule:: 2022-10-14T17:16:57.806Z
|
||||
card-last-reviewed:: 2022-10-04T12:16:57.806Z
|
||||
card-last-score:: 5
|
||||
- A **Foreign Key** is an attribute, or a set of attributes, within one table that matches or **links to** a **candidate key** of some other table (possibly the same table).
|
||||
- More formally:
|
||||
- Given relations $r_1$ and $r_2$, a **foreign key** of $r_2$ is an attribute (or set of attributes) in $r_2$ where that attribute is a **candidate key** in $r_1$. Relations $r_1$ and $r_2$ may be the same relations.
|
||||
- #### Foreign Key Terminology
|
||||
- The **parent**, **master**, or **referenced** table is the relation containing the candidate key(s).
|
||||
- The **child** or **referencing** table / relation is the relation containing the foreign key.
|
||||
-
|
||||
@ -0,0 +1,204 @@
|
||||
- #[[CT230 - Database Systems I]]
|
||||
- **Previous Topic:** [[Database System Introduction]]
|
||||
- **Next Topic:** [[Introduction to SQL & DDL]]
|
||||
- **Relevant Slides:** 
|
||||
-
|
||||
- Why learn about relational DBMS?
|
||||
- 90% of industry / enterprise / business applications are still relational DBMS or relational DBMS with extensions (e.g., OO Relational).
|
||||
- The majority of industry applications require:
|
||||
- **Correctness**
|
||||
- **Completeness**
|
||||
- **Efficiency** (Complex optimisation techniques & complex indexing structures).
|
||||
- Relational DBMS provide this.
|
||||
-
|
||||
- What is the **Relational Data Model**? #card
|
||||
card-last-interval:: 21.53
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-12-06T08:01:57.584Z
|
||||
card-last-reviewed:: 2022-11-14T20:01:57.584Z
|
||||
card-last-score:: 3
|
||||
- The **Relational Data Model** consists of collections of **relations** (often called *tables*) where each relation contains **tuples** (*rows*) and **attributes** (*columns*).
|
||||
- The relational data model is closely related to the file system model.
|
||||
- Relations are named.
|
||||
- What is a **relation**? #card
|
||||
card-last-interval:: 31.36
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-11-20T16:24:50.257Z
|
||||
card-last-reviewed:: 2022-10-20T08:24:50.257Z
|
||||
card-last-score:: 5
|
||||
- A table.
|
||||
- What are **attributes**? #card
|
||||
card-last-interval:: 100.92
|
||||
card-repeats:: 5
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2023-02-23T18:22:23.155Z
|
||||
card-last-reviewed:: 2022-11-14T20:22:23.156Z
|
||||
card-last-score:: 5
|
||||
- **Attributes** are columns.
|
||||
- Columns / attributes are ^^almost always fixed^^ and do not change.
|
||||
- What are **tuples**? #card
|
||||
card-last-interval:: 29.26
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-12-13T22:48:34.835Z
|
||||
card-last-reviewed:: 2022-11-14T16:48:34.835Z
|
||||
card-last-score:: 5
|
||||
- **Tuples** are rows.
|
||||
- Rows contain the data.
|
||||
- There is a variable number of rows.
|
||||
- What is the **cardinality** of a relation? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-11-15T00:00:00.000Z
|
||||
card-last-reviewed:: 2022-11-14T16:51:27.460Z
|
||||
card-last-score:: 1
|
||||
- The ^^number of tuples in a relation^^ is referred to as the **cardinality** of that relation.
|
||||
-
|
||||
- ## Attributes / Columns
|
||||
- Each attribute belongs to **one** *domain* and has a single:
|
||||
- Name
|
||||
- Data Type
|
||||
- Format
|
||||
- ### Naming Columns #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-11-17T15:34:15.662Z
|
||||
card-last-reviewed:: 2022-10-20T08:34:15.663Z
|
||||
card-last-score:: 5
|
||||
- Case is **not** significant in SQL.
|
||||
- No spaces allowed.
|
||||
- No reserved keywords (e.g., date) allowed.
|
||||
- Choose meaningful variable names.
|
||||
- If given the names of relations and attributes, use ^^exactly^^ what you are given.
|
||||
- ### Data Types
|
||||
- You must ^^specify the **data type**^^ of all attributes (columns) defined.
|
||||
- Common data types used include:
|
||||
- **varchar(N)**, where **N** is an integer - used for strings.
|
||||
- date
|
||||
- int
|
||||
- double
|
||||
- You often must specify the size - especially for integers and strings
|
||||
- 
|
||||
- ### NULL
|
||||
- What are **null-valued attributes**? #card
|
||||
card-last-interval:: 29.26
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-12-13T22:48:31.350Z
|
||||
card-last-reviewed:: 2022-11-14T16:48:31.350Z
|
||||
card-last-score:: 5
|
||||
- **Null-valued attributes** are what occurs when the values of some attribute within a particular tuple may be unknown or may not apply to that particular tuple. A **null value** is used for these cases.
|
||||
- **NULL** is a special marker used in SQL to denote the ^^absence of a value.^^
|
||||
- In some cases, we wish to allow the possibility of a `NULL` value although they will often require extra handling (e.g., checking `if == NULL`).
|
||||
- In other cases, we want to prevent `NULL` from being entered as a value and specify `NOT NULL` as a **constraint** on data entry.
|
||||
- ### Atomic Attributes
|
||||
- What is an **atomic attribute**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-12-18T07:51:31.019Z
|
||||
card-last-reviewed:: 2022-11-14T16:51:31.019Z
|
||||
card-last-score:: 5
|
||||
- An **atomic attribute** is an attribute which contains a ^^single value of the appropriate type^^, generally meaning, "no repeating values of the same type".
|
||||
- The relational model should **only** have atomic values.
|
||||
- ### Composite Attributes
|
||||
- What is a **composite attribute**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-12-18T07:52:00.872Z
|
||||
card-last-reviewed:: 2022-11-14T16:52:00.872Z
|
||||
card-last-score:: 5
|
||||
- A **composite attribute** is an attribute that is composed of several atomic attributes.
|
||||
- E.g., `Name = FirstName, Middle Initial, Surname`.
|
||||
- We often want to decompose a composite attribute into atomic attributes unless there is a very good reason not to.
|
||||
- ### Multi-Valued Attributes
|
||||
- What is a **multi-valued attribute**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-11-15T00:00:00.000Z
|
||||
card-last-reviewed:: 2022-11-14T16:33:27.470Z
|
||||
card-last-score:: 1
|
||||
- A **multi-valued attribute** is an attribute which has lower and upper bounds on the number of values for an individual entry.
|
||||
- The ^^opposite of an atomic attribute.^^
|
||||
- The relational model should **not** store multi-valued attributes.
|
||||
- Database design / redesign should be used to deal with this issue by creating more attributes (columns) or more tables.
|
||||
- ### Derived Attributes
|
||||
- What are **derived attributes**? #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-12-12T23:52:22.646Z
|
||||
card-last-reviewed:: 2022-11-14T16:52:22.646Z
|
||||
card-last-score:: 3
|
||||
- A **derived attribute** is an attribute whose value can be determined from another attribute.
|
||||
- E.g., you can derive age from birthdate.
|
||||
- It is a good idea to not directly store attribute which can be derived from other attributes.
|
||||
-
|
||||
- ## Collection of Relations
|
||||
- A Relational Data Model consists of a collection of relations (tables).
|
||||
- Tables are **cross-linked**.
|
||||
-
|
||||
- A relational database usually contains many relations (tables) rather than storing all data in one single relation.
|
||||
- What is a **Relational Schema**? #card
|
||||
card-last-interval:: 19.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-12-04T03:03:56.818Z
|
||||
card-last-reviewed:: 2022-11-14T20:03:56.818Z
|
||||
card-last-score:: 3
|
||||
- A **relational schema**, $R$, is the ^^definition of a **table** in the database.^^ It can be denoted by listing the table name and the attributes:
|
||||
- $$R=\{A_1,A_2,...,A_n\}$$
|
||||
- where $A_i$ is an attribute.
|
||||
- E.g., with $n=3$, `works_on(essn, pno, hours)`.
|
||||
- ## Linking Tables
|
||||
- Two ^^extremely important concepts^^ within the relational model which allows tables to be linked & cross-referenced are:
|
||||
- **Primary Key** attributes.
|
||||
- **Foreign Key** attributes.
|
||||
-
|
||||
- ### Primary Keys
|
||||
- Fundamental concept of **Primary Keys**: #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-11-17T15:34:03.291Z
|
||||
card-last-reviewed:: 2022-10-20T08:34:03.291Z
|
||||
card-last-score:: 5
|
||||
- ^^All tuples (rows) in a relation must be **distinct**.^^
|
||||
- To ensure this, we must have one or more attributes / columns whose data values will ^^always be unique for each tuple^^ - these attributes are called **key attributes** and are used to identify a tuple in the relation.
|
||||
- There may be a few possibilities for the **primary key** - these are called **Candidate Keys**.
|
||||
- One candidate key is ultimately chosen as the primary key during the Design Stage.
|
||||
- What is a **Primary Key**? #card
|
||||
card-last-interval:: 23.43
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.42
|
||||
card-next-schedule:: 2022-12-08T02:44:46.959Z
|
||||
card-last-reviewed:: 2022-11-14T16:44:46.960Z
|
||||
card-last-score:: 5
|
||||
- A **primary key** is defined as one or more attributes per table where:
|
||||
- there can only be one such primary key per table
|
||||
- the primary key can never contain the `NULL` value
|
||||
- all values entered for the primary key must be unique (no duplicates across the rows)
|
||||
- Often, primary keys are used as indices.
|
||||
- We use the convention (in writing) that attribute which form primary keys are $\text{\underline{underlined}}$.
|
||||
-
|
||||
- ### Foreign Keys
|
||||
- What is a **Foreign Key**? #card
|
||||
card-last-interval:: 23.43
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.42
|
||||
card-next-schedule:: 2022-12-08T02:52:18.585Z
|
||||
card-last-reviewed:: 2022-11-14T16:52:18.585Z
|
||||
card-last-score:: 3
|
||||
- A **Foreign Key** is an attribute, or a set of attributes, within one table that matches or **links to** a **candidate key** of some other table (possibly the same table).
|
||||
- More formally:
|
||||
- Given relations $r_1$ and $r_2$, a **foreign key** of $r_2$ is an attribute (or set of attributes) in $r_2$ where that attribute is a **candidate key** in $r_1$. Relations $r_1$ and $r_2$ may be the same relations.
|
||||
- #### Foreign Key Terminology
|
||||
- The **parent**, **master**, or **referenced** table is the relation containing the candidate key(s).
|
||||
- The **child** or **referencing** table / relation is the relation containing the foreign key.
|
||||
-
|
||||
@ -0,0 +1,204 @@
|
||||
- #[[CT230 - Database Systems I]]
|
||||
- **Previous Topic:** [[Database System Introduction]]
|
||||
- **Next Topic:** [[Introduction to SQL & DDL]]
|
||||
- **Relevant Slides:** 
|
||||
-
|
||||
- Why learn about relational DBMS?
|
||||
- 90% of industry / enterprise / business applications are still relational DBMS or relational DBMS with extensions (e.g., OO Relational).
|
||||
- The majority of industry applications require:
|
||||
- **Correctness**
|
||||
- **Completeness**
|
||||
- **Efficiency** (Complex optimisation techniques & complex indexing structures).
|
||||
- Relational DBMS provide this.
|
||||
-
|
||||
- What is the **Relational Data Model**? #card
|
||||
card-last-interval:: 21.53
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-12-06T08:01:57.584Z
|
||||
card-last-reviewed:: 2022-11-14T20:01:57.584Z
|
||||
card-last-score:: 3
|
||||
- The **Relational Data Model** consists of collections of **relations** (often called *tables*) where each relation contains **tuples** (*rows*) and **attributes** (*columns*).
|
||||
- The relational data model is closely related to the file system model.
|
||||
- Relations are named.
|
||||
- What is a **relation**? #card
|
||||
card-last-interval:: 31.36
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-11-20T16:24:50.257Z
|
||||
card-last-reviewed:: 2022-10-20T08:24:50.257Z
|
||||
card-last-score:: 5
|
||||
- A table.
|
||||
- What are **attributes**? #card
|
||||
card-last-interval:: 100.92
|
||||
card-repeats:: 5
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2023-02-23T18:22:23.155Z
|
||||
card-last-reviewed:: 2022-11-14T20:22:23.156Z
|
||||
card-last-score:: 5
|
||||
- **Attributes** are columns.
|
||||
- Columns / attributes are ^^almost always fixed^^ and do not change.
|
||||
- What are **tuples**? #card
|
||||
card-last-interval:: 29.26
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-12-13T22:48:34.835Z
|
||||
card-last-reviewed:: 2022-11-14T16:48:34.835Z
|
||||
card-last-score:: 5
|
||||
- **Tuples** are rows.
|
||||
- Rows contain the data.
|
||||
- There is a variable number of rows.
|
||||
- What is the **cardinality** of a relation? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.8
|
||||
card-next-schedule:: 2022-11-15T00:00:00.000Z
|
||||
card-last-reviewed:: 2022-11-14T16:51:27.460Z
|
||||
card-last-score:: 1
|
||||
- The ^^number of tuples in a relation^^ is referred to as the **cardinality** of that relation.
|
||||
-
|
||||
- ## Attributes / Columns
|
||||
- Each attribute belongs to **one** *domain* and has a single:
|
||||
- Name
|
||||
- Data Type
|
||||
- Format
|
||||
- ### Naming Columns #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-11-17T15:34:15.662Z
|
||||
card-last-reviewed:: 2022-10-20T08:34:15.663Z
|
||||
card-last-score:: 5
|
||||
- Case is **not** significant in SQL.
|
||||
- No spaces allowed.
|
||||
- No reserved keywords (e.g., date) allowed.
|
||||
- Choose meaningful variable names.
|
||||
- If given the names of relations and attributes, use ^^exactly^^ what you are given.
|
||||
- ### Data Types
|
||||
- You must ^^specify the **data type**^^ of all attributes (columns) defined.
|
||||
- Common data types used include:
|
||||
- **varchar(N)**, where **N** is an integer - used for strings.
|
||||
- date
|
||||
- int
|
||||
- double
|
||||
- You often must specify the size - especially for integers and strings
|
||||
- 
|
||||
- ### NULL
|
||||
- What are **null-valued attributes**? #card
|
||||
card-last-interval:: 29.26
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-12-13T22:48:31.350Z
|
||||
card-last-reviewed:: 2022-11-14T16:48:31.350Z
|
||||
card-last-score:: 5
|
||||
- **Null-valued attributes** are what occurs when the values of some attribute within a particular tuple may be unknown or may not apply to that particular tuple. A **null value** is used for these cases.
|
||||
- **NULL** is a special marker used in SQL to denote the ^^absence of a value.^^
|
||||
- In some cases, we wish to allow the possibility of a `NULL` value although they will often require extra handling (e.g., checking `if == NULL`).
|
||||
- In other cases, we want to prevent `NULL` from being entered as a value and specify `NOT NULL` as a **constraint** on data entry.
|
||||
- ### Atomic Attributes
|
||||
- What is an **atomic attribute**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-12-18T07:51:31.019Z
|
||||
card-last-reviewed:: 2022-11-14T16:51:31.019Z
|
||||
card-last-score:: 5
|
||||
- An **atomic attribute** is an attribute which contains a ^^single value of the appropriate type^^, generally meaning, "no repeating values of the same type".
|
||||
- The relational model should **only** have atomic values.
|
||||
- ### Composite Attributes
|
||||
- What is a **composite attribute**? #card
|
||||
card-last-interval:: 33.64
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.9
|
||||
card-next-schedule:: 2022-12-18T07:52:00.872Z
|
||||
card-last-reviewed:: 2022-11-14T16:52:00.872Z
|
||||
card-last-score:: 5
|
||||
- A **composite attribute** is an attribute that is composed of several atomic attributes.
|
||||
- E.g., `Name = FirstName, Middle Initial, Surname`.
|
||||
- We often want to decompose a composite attribute into atomic attributes unless there is a very good reason not to.
|
||||
- ### Multi-Valued Attributes
|
||||
- What is a **multi-valued attribute**? #card
|
||||
card-last-interval:: -1
|
||||
card-repeats:: 1
|
||||
card-ease-factor:: 2.46
|
||||
card-next-schedule:: 2022-11-15T00:00:00.000Z
|
||||
card-last-reviewed:: 2022-11-14T16:33:27.470Z
|
||||
card-last-score:: 1
|
||||
- A **multi-valued attribute** is an attribute which has lower and upper bounds on the number of values for an individual entry.
|
||||
- The ^^opposite of an atomic attribute.^^
|
||||
- The relational model should **not** store multi-valued attributes.
|
||||
- Database design / redesign should be used to deal with this issue by creating more attributes (columns) or more tables.
|
||||
- ### Derived Attributes
|
||||
- What are **derived attributes**? #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-12-12T23:52:22.646Z
|
||||
card-last-reviewed:: 2022-11-14T16:52:22.646Z
|
||||
card-last-score:: 3
|
||||
- A **derived attribute** is an attribute whose value can be determined from another attribute.
|
||||
- E.g., you can derive age from birthdate.
|
||||
- It is a good idea to not directly store attribute which can be derived from other attributes.
|
||||
-
|
||||
- ## Collection of Relations
|
||||
- A Relational Data Model consists of a collection of relations (tables).
|
||||
- Tables are **cross-linked**.
|
||||
-
|
||||
- A relational database usually contains many relations (tables) rather than storing all data in one single relation.
|
||||
- What is a **Relational Schema**? #card
|
||||
card-last-interval:: 19.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.32
|
||||
card-next-schedule:: 2022-12-04T03:03:56.818Z
|
||||
card-last-reviewed:: 2022-11-14T20:03:56.818Z
|
||||
card-last-score:: 3
|
||||
- A **relational schema**, $R$, is the ^^definition of a **table** in the database.^^ It can be denoted by listing the table name and the attributes:
|
||||
- $$R=\{A_1,A_2,...,A_n\}$$
|
||||
- where $A_i$ is an attribute.
|
||||
- E.g., with $n=3$, `works_on(essn, pno, hours)`.
|
||||
- ## Linking Tables
|
||||
- Two ^^extremely important concepts^^ within the relational model which allows tables to be linked & cross-referenced are:
|
||||
- **Primary Key** attributes.
|
||||
- **Foreign Key** attributes.
|
||||
-
|
||||
- ### Primary Keys
|
||||
- Fundamental concept of **Primary Keys**: #card
|
||||
card-last-interval:: 28.3
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.66
|
||||
card-next-schedule:: 2022-11-17T15:34:03.291Z
|
||||
card-last-reviewed:: 2022-10-20T08:34:03.291Z
|
||||
card-last-score:: 5
|
||||
- ^^All tuples (rows) in a relation must be **distinct**.^^
|
||||
- To ensure this, we must have one or more attributes / columns whose data values will ^^always be unique for each tuple^^ - these attributes are called **key attributes** and are used to identify a tuple in the relation.
|
||||
- There may be a few possibilities for the **primary key** - these are called **Candidate Keys**.
|
||||
- One candidate key is ultimately chosen as the primary key during the Design Stage.
|
||||
- What is a **Primary Key**? #card
|
||||
card-last-interval:: 23.43
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.42
|
||||
card-next-schedule:: 2022-12-08T02:44:46.959Z
|
||||
card-last-reviewed:: 2022-11-14T16:44:46.960Z
|
||||
card-last-score:: 5
|
||||
- A **primary key** is defined as one or more attributes per table where:
|
||||
- there can only be one such primary key per table
|
||||
- the primary key can never contain the `NULL` value
|
||||
- all values entered for the primary key must be unique (no duplicates across the rows)
|
||||
- Often, primary keys are used as indices.
|
||||
- We use the convention (in writing) that attribute which form primary keys are $\text{\underline{underlined}}$.
|
||||
-
|
||||
- ### Foreign Keys
|
||||
- What is a **Foreign Key**? #card
|
||||
card-last-interval:: 23.43
|
||||
card-repeats:: 4
|
||||
card-ease-factor:: 2.42
|
||||
card-next-schedule:: 2022-12-08T02:52:18.585Z
|
||||
card-last-reviewed:: 2022-11-14T16:52:18.585Z
|
||||
card-last-score:: 3
|
||||
- A **Foreign Key** is an attribute, or a set of attributes, within one table that matches or **links to** a **candidate key** of some other table (possibly the same table).
|
||||
- More formally:
|
||||
- Given relations $r_1$ and $r_2$, a **foreign key** of $r_2$ is an attribute (or set of attributes) in $r_2$ where that attribute is a **candidate key** in $r_1$. Relations $r_1$ and $r_2$ may be the same relations.
|
||||
- #### Foreign Key Terminology
|
||||
- The **parent**, **master**, or **referenced** table is the relation containing the candidate key(s).
|
||||
- The **child** or **referencing** table / relation is the relation containing the foreign key.
|
||||
-
|
||||
Reference in New Issue
Block a user