uni/Introduction to SQL & DDL.md at 9694cc81d803692f51940714f97805d0509d6c63

aindreas/uni

Fork 0

Files

Andrew 1f7d812b98 Rename year directories to allow natural ordering

2023-12-20 03:57:27 +00:00

17 KiB

Raw Blame History

#CT230 - Database Systems I
Previous Topic: The Relational Model
Next Topic: SQL DML Statement
Relevant Slides:
SQL
- What is SQL? #card card-last-interval:: 31.36 card-repeats:: 4 card-ease-factor:: 2.8 card-next-schedule:: 2022-12-18T17:47:35.469Z card-last-reviewed:: 2022-11-17T09:47:35.470Z card-last-score:: 5
  - Structured Query Language (SQL) is a special-purpose programming language for relational database systems.
- Features of SQL
  - SQL is based on relational algebra.
    - All relational, set, and hybrid operators are supported.
    - SQL also has additional operators to allow easier query development.
  - SQL has been standardised since 1987.
  - The American National Standards Institute (ANSI) and International Organization for Standardization (ISO) form SQL standard committees. Many vendors also take part.
  - Recent standards include XML-related features in addition to many others, including JSON data types.
- ANSI/ISO SQL
  - Despite standards, there can be a lack of portability between database systems due to:
    - Complexity & size of standards (not all vendors will implement all of the standard).
    - The vendor may want to keep the syntax consistent with their other software products / OS or develop features to support their user base.
    - The vendor may want to maintain backward compatibility.
    - The vendor may want to maintain "Vendor lock-in".
  - What is the standardised SQL syntax comprised of? #card card-last-interval:: 10.6 card-repeats:: 3 card-ease-factor:: 2.56 card-next-schedule:: 2022-11-25T06:29:02.836Z card-last-reviewed:: 2022-11-14T16:29:02.836Z card-last-score:: 5
    - The standardised SQL syntax comprises 3 components:
      - DDL - Data Definition Language
      - DCL - Data Control Language
      - DML - Data Manipulation Language
  - DCL: Data Control Language
    - What is DCL used for? #card card-last-interval:: 31.36 card-repeats:: 4 card-ease-factor:: 2.8 card-next-schedule:: 2022-12-16T04:21:50.434Z card-last-reviewed:: 2022-11-14T20:21:50.434Z card-last-score:: 5
      - Data Control Language is used to control access to the database & to database relations.
      - It is the role of the database administrator.
      - Very important in multi-user systems.
    - What are the typical DCL commands? #card card-last-interval:: 41.44 card-repeats:: 5 card-ease-factor:: 2.18 card-next-schedule:: 2022-12-26T06:18:39.799Z card-last-reviewed:: 2022-11-14T20:18:39.800Z card-last-score:: 5
      - GRANT REVOKE
      - These can be used to:
        
        grant / revoke access to the database.
        
        grant / revoke access to individual relations.
  - DDL: Data Definition Language
    - What is DDL? #card card-last-interval:: 86.42 card-repeats:: 5 card-ease-factor:: 2.66 card-next-schedule:: 2023-02-09T06:22:06.927Z card-last-reviewed:: 2022-11-14T20:22:06.927Z card-last-score:: 5
      - Data Definition Language is a standardised language to ^^define the schema of a database.^^
      - It's the back-end of "design" options on the Interface (e.g., Create options).
    - What are the typical DDL commands? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.22 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T16:36:00.957Z card-last-score:: 1
      - The typical DDL tasks include creating, altering, and removing database objects such as tables & indexes.
      - Common DDL keywords include:
        
        CREATE ALTER DROP ADD CONSTRAINT
    - Create a table, its indexes, & constraints
      - Steps:
        
        Specify table (relation) name.
        
        For each attribute in the table, specify Attribute Name, Data Type, and any constraints.
        
        Specify the Primary Key of the table: choose one or more attributes.
        
        Specify Foreign Keys if they exist and assuming that the attributes & table you are referencing exist (you may have to return to this step).
        
        Steps 1-3 ^^must be completed for all tables.^^
    - Data Types
      - The main data types are strings, numeric, and date/time.
      - Strings
        
        What can strings contain? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:37:34.017Z card-last-reviewed:: 2022-11-14T16:37:34.018Z card-last-score:: 5
        
        Strings can contain ^^letters, numbers, & special characters.^^
        
        Types of string: #card card-last-interval:: 23.43 card-repeats:: 4 card-ease-factor:: 2.42 card-next-schedule:: 2022-12-08T06:03:14.822Z card-last-reviewed:: 2022-11-14T20:03:14.822Z card-last-score:: 3
        
        CHAR(size) is a string of fixed length. size can be from 0 to 255 - the default is 1.
        
        VARCHAR(size) is a string of variable length. size can be from 0 to 65,535.
        
        if size is not specified, it is unlimited
        
        TEXT is the same thing as VARCHAR except it is unlimited by default, and takes no argument size.
      - Date/Time
        
        Types of date/time: #card card-last-interval:: 47.41 card-repeats:: 5 card-ease-factor:: 2.28 card-next-schedule:: 2023-01-01T05:18:44.919Z card-last-reviewed:: 2022-11-14T20:18:44.919Z card-last-score:: 3
        
        DATE Format: YYYY-MM_DD
        
        TIME Format: hh:mm:ss
        
        DATETIME Format: YYYY-MM-DD hh:mm:ss
        
        YEAR A year in four-digit format
      - Numeric
        
        The maximum size value is 255.
        
        MySQL supports unsigned numeric types but not all DBMS do.
        
        Types of numerics: #card card-last-interval:: 19.01 card-repeats:: 4 card-ease-factor:: 2.18 card-next-schedule:: 2022-12-03T16:48:07.382Z card-last-reviewed:: 2022-11-14T16:48:07.383Z card-last-score:: 3
        
        INTEGERS - See next block.
        
        BOOL / BOOLEAN - 0 is False; non-zero is True.
        
        FLOAT - A floating-point number. 4 bytes, single precision.
        
        DOUBLE - A floating-point number. 8 bytes, double precision.
        
        DECIMAL(size, d) / DEC(size,d) - An exact, fixed-point number.
        
        size = total number of digits (max 65, default 10)
        
        d = number of digits after the decimal point (max 30, default 0)
      - Integers
        
        Types of integers:
        
        | Type | Bytes | Range | | TINYINT | 1 | -128 to 127 | | SMALLINT | 2 | -32,768 to 32,767 | | MEDIUMINT | 3 | -8,388,608 to 8,388,607 | | INT | 4| -2,147,483,648 to 2,147,483,647 | | BIGINT | 8 | -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 |
        
        ^^Note:^^ the number in brackets next to integers only refers to the number of digits to display, not size.
      - Others
        
        Unicode char/string
        
        Binary
        
        Blob, Json, etc.
  - DML: Data Manipulation Language
    - What is DML? #card card-last-interval:: 25.4 card-repeats:: 4 card-ease-factor:: 2.52 card-next-schedule:: 2022-12-12T18:47:31.780Z card-last-reviewed:: 2022-11-17T09:47:31.780Z card-last-score:: 5
      - Data Manipulation Language is a standardised language used for ^^adding, deleting, & modifying data in a database.^^
    - What are the typical DML commands? #card card-last-interval:: 15.05 card-repeats:: 4 card-ease-factor:: 1.94 card-next-schedule:: 2022-11-29T17:40:29.100Z card-last-reviewed:: 2022-11-14T16:40:29.100Z card-last-score:: 3
      - INSERT -- insert data SELECT -- query (select) data UPDATE -- update data DELETE -- delete data
Autonumber
- What does AUTO_INCREMENT do in MySQL? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T03:03:50.803Z card-last-reviewed:: 2022-11-14T20:03:50.803Z card-last-score:: 5
  - Specifying an attribute to AUTO_INCREMENT tells the DBMS to ^^generate a number automatically when a new tuple is inserted into a table.^^
  - Often, this is used for an "artificial" primary key value which is needed to ensure that we have a primary key, but has no meaning for the data being stored.
  - Using AUTO_INCREMENT means that the DBMS takes care of inserting a unique value automatically every time a new tuple is inserted.
  - By default, AUTO_INCREMENT is 1, and is incremented by 1 for each new tuple inserted.
Constraints
- Types of Constraints
  - Foreign Keys
    - What is the syntax for specifying Foreign Keys? #card card-last-interval:: 41.44 card-repeats:: 5 card-ease-factor:: 2.18 card-next-schedule:: 2022-12-26T06:21:18.467Z card-last-reviewed:: 2022-11-14T20:21:18.468Z card-last-score:: 3
      - FOREIGN KEY (attributename) REFERENCES tablename(attributename)
      - You need to specify:
        
        The keyword FOREIGN KEY to indicate that it is a foreign key constraint.
        
        The attribute name(s) that will identify the foreign keys in the current table.
        
        If there is more than one attribute, they should be separated by commas.
        
        Attribute names should be enclosed in brackets.
        
        The keyword REFERENCES to specify the attribute that the foreign key references.
        
        The table name and the attribute name of the attribute being referenced by the foreign key.
        
        Again, the attribute name(s)should be in brackets.
        
        The table name should be outside the brackets.
    - ^^You cannot create a foreign key link unless the attribute that it is referencing exists.^^
    - Using ALTER to Modify Design
      - Remember: You cannot create a foreign key link unless the attribute it's referencing already exists.
      - If you want to create everything but the foreign keys initially, you can add a foreign key later using the ALTER TABLE command
      - Syntax for ALTER Command
        
        To add a constraint:
        
        ALTER TABLE tablename ADD CONSTRAINT constraintname FOREIGN KEY (attributename) REFERENCES tablename(attribute name);
        
        To add an attribute (column) constraint:
        
        ALTER TABLE tablename ADD attributename DATATYPE;
  - Domain Constraints
    id:: 6321ba81-0b92-447e-9c6f-1953528d51a8
    - What is the Domain Constraint? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.6 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T16:38:56.391Z card-last-score:: 1
      - The value of each attribute A must be an atomic value from the domain dom(A).
        
        Essentially: ^^the data types & formats must match to that specified.^^
  - Entity Integrity Constraints (Primary Key Constraints)
    id:: 6321bafc-6bfc-42da-96a9-f05bcfdff9ba
    - What is the Primary Key / Entity Integrity Constraint? #card card-last-interval:: 31.36 card-repeats:: 4 card-ease-factor:: 2.8 card-next-schedule:: 2022-12-16T00:47:09.544Z card-last-reviewed:: 2022-11-14T16:47:09.544Z card-last-score:: 5
      - The primary key should uniquely identify each tuple in a relation.
      - This means:
        
        No duplicate values allowed for the primary key
        
        No NULLvalues allowed for the primary key
    - Note: NULL values may possibly also not be permitted for other attributes.
      - We often see this constraint when filling out forms online ("*required") and the constraint is often necessary for non-key attributes.
      - However, we should be careful to only add NOT NULL constraints in the databases when they are really necessary.
  - Referential Integrity Constraints
    - What are Referential Integrity Constraints? #card card-last-score:: 1 card-repeats:: 1 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-interval:: -1 card-ease-factor:: 2.56 card-last-reviewed:: 2022-11-14T20:19:00.925Z
      - Referential Integrity Constraints are specified between two relations and require the concept of a foreign key. The constraint ensures that ^^the database must not contain any unmatched foreign keys.^^
      - Therefore, a relationship involving foreign keys must be between attributes of the ^^same type & size.^^
      - In addition, a value for a foreign key attribute must exist already as a candidate key value.
      - Essentially: "no unmatched foreign keys".
  - Semantic Integrity Constraints
    - What are Semantic Integrity Constraints? #card card-last-interval:: 56.69 card-repeats:: 5 card-ease-factor:: 2.42 card-next-schedule:: 2023-01-07T03:37:12.551Z card-last-reviewed:: 2022-11-11T11:37:12.551Z card-last-score:: 5
      - Semantic Integrity Constraints ensure that the data entered into a row reflects an allowable value for that row. The value must be within the domain, or allowable set of values, for that column.
    - How are Semantic Integrity Constraints specified? #card card-last-interval:: -1 card-repeats:: 1 card-ease-factor:: 2.6 card-next-schedule:: 2022-11-15T00:00:00.000Z card-last-reviewed:: 2022-11-14T16:42:45.174Z card-last-score:: 1
      - Semantic Integrity Constraints are specified & enforced using a constraint specification language.
    - What are the two types of Semantic Integrity Constraints? #card card-last-interval:: 4 card-repeats:: 2 card-ease-factor:: 2.18 card-next-schedule:: 2022-11-25T13:05:15.346Z card-last-reviewed:: 2022-11-21T13:05:15.347Z card-last-score:: 3
      - State Constraints: Constrain an entity to being in certain states.
      - Transition Constraints: Constrain an entity to only being updated in certain ways.
- Setting Constraints
  - Domain Constraints are set automatically once the data type is chosen.
  - Entity Constraints are also set automatically once a primary key has been chosen.
  - Usually default constraints are set for foreign keys, but these can be changed.
- Update Operations & Constraint Violations
  - The DBMS must check that the constraints are not violated whenever update operations are applied.
  - Insert Operation
    - What does the Insert Operation do? #card card-last-interval:: 31.36 card-repeats:: 4 card-ease-factor:: 2.8 card-next-schedule:: 2022-12-16T00:47:14.600Z card-last-reviewed:: 2022-11-14T16:47:14.600Z card-last-score:: 5
      - The Insert Operation provides a list of attribute values for a new tuple t that is to be inserted into a relation R.
        
        This can happen directly via the interface or via the query.
      - If a constraint is violated, the DBMS will reject the insertion - usually with an explanation.
  - Delete Operation
    - How can a Delete Operation violate constraints? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-13T03:03:33.858Z card-last-reviewed:: 2022-11-14T20:03:33.859Z card-last-score:: 5
      - A delete operation can only violate integrity constraints, i.e., if the tuple being deleted is referenced by the foreign key from other tuples.
      - The DBMS can:
        
        reject deletion, usually within an explanation.
        
        attempt to cascade deletion.
        
        modify referencing attribute.
  - Update Operation
    card-last-score:: 1 card-repeats:: 1 card-next-schedule:: 2022-10-07T23:00:00.000Z card-last-interval:: -1 card-ease-factor:: 2.5 card-last-reviewed:: 2022-10-07T10:32:05.858Z
    - What is an Update Operation? #card card-last-interval:: 8.88 card-repeats:: 3 card-ease-factor:: 2.22 card-next-schedule:: 2022-11-20T08:30:42.712Z card-last-reviewed:: 2022-11-11T11:30:42.713Z card-last-score:: 3
      - An update operation is used to change the values of one or more attributes in a tuple of a table.
      - Issues already discussed with insert & delete could arise with this operation, specifically:
        
        If a primary key is modified, that's essentially the same as deleting one tuple and inserting another tuple in its place.
        
        If a foreign key is modified, the DBMS must ensure that the new value refers to an existing tuple in the reference relation.
  - Cascade Update & Delete
    - Whenever tuples in the referenced (master) table are deleted or updated, the respective tuples of the referencing (child) table with a matching foreign key column will be deleted or updated as well.
    - Note that if cascading DELETE is turned on, there could be many deletions performed with a single query such as:
      - DELETE FROM employee WHERE ssn = 12345678;

17 KiB

Raw Blame History

SQL

Features of SQL

ANSI/ISO SQL

DCL: Data Control Language

DDL: Data Definition Language

Create a table, its indexes, & constraints

Data Types

DML: Data Manipulation Language

Autonumber

Constraints

Types of Constraints

Foreign Keys

Using `ALTER` to Modify Design

Syntax for `ALTER` Command

Domain Constraints

Entity Integrity Constraints (Primary Key Constraints)

Referential Integrity Constraints

Semantic Integrity Constraints

Setting Constraints

Update Operations & Constraint Violations

Insert Operation

Delete Operation

Update Operation

Cascade Update & Delete

17 KiB Raw Blame History

SQL

Features of SQL

ANSI/ISO SQL

DCL: Data Control Language

DDL: Data Definition Language

Create a table, its indexes, & constraints

Data Types

DML: Data Manipulation Language

Autonumber

Constraints

Types of Constraints

Foreign Keys

Using ALTER to Modify Design

Syntax for ALTER Command

Domain Constraints

Entity Integrity Constraints (Primary Key Constraints)

Referential Integrity Constraints

Semantic Integrity Constraints

Setting Constraints

Update Operations & Constraint Violations

Insert Operation

Delete Operation

Update Operation

Cascade Update & Delete

17 KiB

Raw Blame History

Using `ALTER` to Modify Design

Syntax for `ALTER` Command