1. Using Relational Databases and SQL
Lecture 10:
Data Definition Language
Steven Emory
Department of Computer Science
California State University, Los Angeles

2. Miscellany
For today’s topic, use the Lyrics database

3. Topics for Today Data Types (Appendix)
Creating Tables (Pages 188 – 190)‏
Deleting Tables (Page 190)‏
Adding Columns (Pages 190 – 191)‏
Deleting Columns (Page 192)‏
Editing Columns (Pages 191 – 192)‏
Identity Columns (Pages 193 – 195)‏
Constraints (Pages 196 – 207)‏

4. Data Types TINYINT(width): 1 byte SMALLINT(width): 2 bytes
MEDIUMINT(width): 3 bytes
INT(width): 4 bytes
BIGINT(width): 8 bytes
FLOAT(n, d): 4 bytes
REAL(n, d): 8 bytes
DATE: 3 bytes
CHAR(n) and VARCHAR(n): Variable bytes

5. Creating Tables Syntax:
CREATE TABLE ( fieldname datatype NULL | NOT NULL, fieldname datatype NULL | NOT NULL, fieldname datatype NULL | NOT NULL );
Each row specifies a column definition
Use NULL or NOT NULL to specify whether or not a column can contain NULL values

6. CREATE TABLE Example Example:
CREATE TABLE Musician ( Musician VARCHAR(32) NOT NULL ); INSERT INTO Musician VALUES(‘Guitarist’); INSERT INTO Musician VALUES(‘Pianist’); INSERT INTO Musician VALUES(‘Drummer’); INSERT INTO Musician VALUES(‘Vocalist’); INSERT INTO Musician VALUES(‘Bassist’);

7. Dropping Tables Syntax: Example: DROP TABLE [IF EXISTS] tablename;
DROP TABLE Artists;
NOTE: BEGIN and ROLLBACK do not work with DROP TABLE

8. Adding Columns Syntaxes:
ALTER TABLE tablename ADD COLUMN column_definition;
ALTER TABLE tablename ADD COLUMN column_definition FIRST;
ALTER TABLE tablename ADD COLUMN column_definition AFTER column_name;

9. Examples
Examples:
ALTER TABLE Musician ADD COLUMN MusicianID INT NOT NULL FIRST;
ALTER TABLE Musician ADD COLUMN Type VARCHAR(16) NULL; INSERT INTO Musician VALUES(‘1’, ‘Guitarist’, ‘Electric’);

10. Dropping Columns Syntax: Example:
ALTER TABLE tablename DROP COLUMN column_name;
Example:
ALTER TABLE Musician DROP COLUMN Type;

11. Editing Columns
MODIFY let’s you change a column’s data definition (without renaming it)
CHANGE does the same thing as MODIFY, but you can also specify a new column name
Syntax:
ALTER TABLE tablename MODIFY fieldname column_definition;
ALTER TABLE tablename CHANGE oldname newname column_definition

12. Examples
Examples:
-- Let’s rename the Musician column to Instrument. ALTER TABLE Musician CHANGE Musician Instrument VARCHAR(32) NOT NULL;
-- Let’s modify the Instrument column string length to make it really short! ALTER TABLE Musician MODIFY Instrument VARCHAR(4) NOT NULL;

13. Constraints
A constraint is any kind of restriction placed on the data inserted into a table
Primary Key Constraints: Enforces uniqueness of data.
Foreign Key Constraints: A value must refer to an existing piece of data.
Default Constraints: Data not specifically inserted will take on default values.
Unique Constraints: Forces data (other than the primary key) to be unique.

14. Primary Key Constraints
CREATE TABLE Syntax:
Can add the keyword PRIMARY key at end of column definition
For more than one column you can use the CONSTRAINT keyword.
ALTER TABLE Syntax:
ALTER TABLE tablename ADD CONSTRAINT constraint_name PRIMARY KEY (field1, field2, ...);

15. Examples
Examples:
CREATE TABLE tablename( field1 INT NOT NULL, field2 INT NOT NULL, CONSTRAINT constraint_name PRIMARY KEY(field1) );
ALTER TABLE Titles ADD CONSTRAINT fk_titles PRIMARY KEY(TitleID);

16. Foreign Key Constraints
Sometimes called integrity constraints
CREATE TABLE Syntax:
CONSTRAINT constraint_name FOREIGN KEY(field1, field2, ...) REFERENCES parent_table(field1, field2, ...)‏
ALTER TABLE Syntax:
ALTER TABLE tablename ADD CONSTRAINT constraint_name FOREIGN KEY (field1, field2, ...) REFERENCES parent_table(field1, field2, ...);

17. Examples
Example:
-- To run the following example, make sure to make the Genre attribute the primary key in the Genre table or else this won’t work! A foreign key must reference a primary key! ALTER TABLE Titles ADD CONSTRAINT fk_titles_genre FOREIGN KEY (Genre) REFERENCES Genre (Genre);

18. Unique Constraints
Use to make one or more columns (other than the primary key) contain only unique values
CREATE TABLE Syntax:
Just add the UNIQUE keyword at the end.
ALTER TABLE Syntax:
ALTER TABLE tablename ADD CONSTRAINT constraint_name UNIQUE (fieldname1, fieldname2, ...);

19. Examples
Examples:
CREATE TABLE login( user_id INT NOT NULL PRIMARY KEY, username VARCHAR(32) NOT NULL UNIQUE, password VARCHAR(32) NOT NULL );
ALTER TABLE login ADD CONSTRAINT uq_username UNIQUE(username);
INSERT INTO login(1, ‘semory’, ‘mypassword’);
INSERT INTO login(2, ‘semory’, ‘anotherpass’);

20. Default Constraints Using CREATE TABLE: Using ALTER TABLE:
After specifying the datatype in the column definition, use the following: DEFAULT value
Using ALTER TABLE:
ALTER TABLE tablename ALTER fieldname SET DEFAULT value;

21. Examples Examples: DROP TABLE login;
CREATE TABLE login( user_id INT NOT NULL PRIMARY KEY, username VARCHAR(32) NOT NULL UNIQUE, password VARCHAR(32) DEFAULT ‘0xk2739’ NOT NULL );
ALTER TABLE SalesPeople ALTER Base SET DEFAULT ;

22. Dropping Constraints
Do not read the book on this! The book’s code will not work! Use the following syntax:
Syntax:
-- To drop a primary key... ALTER TABLE tablename DROP PRIMARY KEY;
-- To drop a foreign key... ALTER TABLE tablename DROP FOREIGN KEY keyname;
-- To drop any other key... ALTER TABLE tablename DROP KEY keyname;

23. Examples
Examples:
-- Drop the fk_titles_genre foreign key in the Titles table. ALTER TABLE Titles DROP FOREIGN KEY fk_titles_genre;
-- Drop the pk_genre primary key in the Genre table. ALTER TABLE Genre DROP PRIMARY KEY pk_genre;
-- Drop the uq_username unique key in the login table. ALTER TABLE login DROP KEY uq_username;

24. Identity Columns Purpose is to auto-generate primary key values
MySQL uses the non-standard keyword AUTO_INCREMENT and you can only define it on the primary key
SQL standard uses GENERATE keyword
Syntax:
fieldname datatype NOT NULL AUTO_INCREMENT

25. Identity Column Example
DELETE FROM Musician;
ALTER TABLE Musician MODIFY Instrument VARCHAR(32) NOT NULL AUTO_INCREMENT;
INSERT INTO Musician VALUES(0, ‘Guitarist’); INSERT INTO Musician VALUES(0, ‘Pianist’); INSERT INTO Musician VALUES(0, ‘Vocalist’); INSERT INTO Musician VALUES(0, ‘Bassist’); INSERT INTO Musician VALUES(0, ‘Drummer’);