Using Relational Databases and SQL Department of Computer Science California State University, Los Angeles Lecture 9: Data Manipulation Language Data Definition Language

Data Manipulation Language Substantially different material than we have been doing. Moving on from just querying existing data

Before We Start When modifying the database data, you are going to make mistakes If you mess up you can recover the original database by dropping the tables and rerunning the original script You can also protect against disasters by using transactions

Before We Start It is easier to use BEGIN and ROLLBACK than to drop the tables and reinstall! Use BEGIN before entering DML commands Use ROLLBACK to undo all changes USE COMMIT to accept all changes

Transactions ACID Atomicity: a transaction should be done fully or not at all Consistency: when transaction is complete, data should be self-consistent; no orphan records or inconsistent totals Isolation: no other users see any part of the transaction until it is complete Durability: when transaction is finished, the results persist

Data Manipulation Language DML for short Contains commands for modifying table data Insertion commands (INSERT INTO) Deletion commands (DELETE) Update commands (UPDATE) Not a query Queries extract data from the database Commands do not extract data from the database

Inserting Records Two syntaxes: INSERT INTO Insert one record at a time INSERT SELECT Insert one or more records at a time

Inserting Records INSERT INTO Syntax -- Form #1: Insert whole record. INSERT INTO tablename VALUES(value1, value2,..., valuen); -- Form #2: Insert partial record. Non-specified fieldnames are assigned default values. INSERT INTO tablename(field1, field2,..., fieldn) VALUES(value1, value2,..., valuen);

Inserting Records INSERT INTO salespeople values(5, "Mary", "Smith", "MSS", , 4) INSERT INTO salespeople (SalesID, FirstName, LastName, Initials, Base) values(5, "Mary", "Smith", "mss", 100);

Inserting Records INSERT SELECT Syntax -- Form #1: Insert whole record. INSERT INTO destination_table SELECT field1, field2,..., fieldn FROM source_tables WHERE conditions; -- Form #2: Insert partial record. Non-specified fieldnames are assigned default values. INSERT INTO destination_table(df1, df2,..., dfn) SELECT sf1, sf2,..., sfn FROM source_tables WHERE conditions;

INSERT INTO Example Example: Add new title “Out of Medication” by the Neurotics. Assign it titleNum 8 and genre alternative. Find the artistid of the Neurotics by looking them up in the artists table.

Insert With A Transaction Begin; Select * from titles; INSERT INTO titles VALUES (8,(SELECT artistID FROM artists WHERE artistname = “the Neurotics”), 'Out of Medication', 1, ' ', “alternative”); Select * from titles; Rollback; Select * from titles;

Deleting Records Deletes one or more rows from a table Can select rows to delete using WHERE clause Without WHERE condition, will delete all rows Two syntaxes Single-Table DELETE Syntax Multi-Table DELETE Syntax

DELETE Syntax Syntax: DELETE FROM tablename WHERE condition;

DELETE Syntax Solutions: -- Delete all records. DELETE FROM testtable; -- Delete all records for people named “Bob” DELETE FROM testtable WHERE name = ‘Bob’; Delete the record you added for ‘Out of Medication‘: DELETE FROM titles WHERE titleName = ‘Out of Medication’

DELETE Syntax Delete all titles by the Neurotics: BEGIN; DELETE FROM titles WHERE artistID = (SELECT artistID FROM artists WHERE artistName = 'the Neurotics')

DELETE Syntax Add a title ‘No Word From You ’ by Word in the genre rap with titleID 100. studioID 3, and UPC INSERT INTO titles VALUES (100, (SELECT artistID FROM artists WHERE artistName = 'Word'), 'No Word From You', 3, ' ', 'rap'); Then SELECT * FROM titles;

DELETE Syntax now delete all titles by Word DELETE FROM titles WHERE artistID = (SELECT artistID FROM artists WHERE artistName = ‘Word’); SELECT * from the table again

DELETE Syntax Delete can lead to orphaned records if misused (a foreign key with no primary key). DELETE FROM salespeople WHERE lastName = ‘Bentley’ Unless the DB is set up to enforce foreign keys by refusing to let you do this, all the studios and members represented by the salesperson contain salesIDs that do not reference any record in the salespeople table

Multi-Table DELETE Syntax Therefore, be careful what you delete! If you delete a record, and that record is referenced somewhere else, you have an orphaned record!

Updating Records To update existing records, you may use one of the following syntaxes: Single-table syntax. Multi-table equi-join syntax. Only equi-join is supported. You may not use any other join syntax (JOIN ON, JOIN USING, etc.)

Updating Records To update existing records: -- Single-table syntax. UPDATE [IGNORE] tablename SET field1 = value1, field2 = value2,... WHERE conditions; -- Multi-table equi-join syntax. UPDATE [IGNORE] tablename1, tablename2,... SET field1 = value1, field2 = value2,... WHERE conditions; -- Multi-table subquery syntax. UPDATE [IGNORE] tablename SET field1 = subquery1, field2 = subquery2,... WHERE conditions;

Updating Records Examples: Bryce Sanders has decided to drop his stage name in favor of his birth name, “Ebenezer Hackensack.” Update the members table accordingly. UPDATE members SET lastname = ‘Hackensack’, firstName = ‘Ebenezer’ WHERE lastName = ‘Sanders’ and firstName = ‘Bryce’ update members set city = "Alvarez" where city = "Alverez";

Updating Records Examples: -- MakeTrax has been bought by Pacific Rim. Update all titles for MakeTrax to show the new Studio information.

Updating Records Examples: begin; UPDATE titles SET StudioID = (SELECT studioID FROM studios WHERE studioName = 'Pacific Rim') WHERE studioID = (SELECT StudioID FROM Studios WHERE StudioName = 'MakeTrax'); select * from titles; rollback;

Updating Records The IGNORE keyword causes the DBMS to ignore updates that would result in primary key duplicates, (instead of producing error messages)

Updating Records CREATE TABLE vehicles( id int primary key, name varchar(30) ); INSERT INTO vehicles values(1, “Moby"); INSERT INTO vehicles values(2, “Morticia"); UPDATE vehicles SET id = 1 WHERE id = 2; ERROR! BEEP! Update is not performed.

Update Ignore INSERT INTO vehicles values(1, “Moby"); INSERT INTO vehicles values(2, “Morticia"); UPDATE IGNORE vehicles SET id = 1 WHERE id = 2; Update is still not performed, but no error messages or beeps.

Data Types Storing data in a database uses up resources Computers store information in bits one bit is equivalent to a switch that is either on or off; two possible values One byte = 8 bits 2 ^ 8 = 256 possible values for one byte

Data Types What happens if you allocate 30 bytes to hold data, but none of the records have more than 20 bytes in that field? What if you allocate 20 bytes, but one of the records has 30 bytes of information in the field? what if you track dates using two digit years, and then a new century starts? Do millions of people get charged negative 100 years of mortgage interest?

Integer Data Types Data Types TINYINT(width): 1 byte SMALLINT(width): 2 bytes MEDIUMINT(width): 3 bytes INT(width): 4 bytes BIGINT(width): 8 bytes

Numeric Data Types Data Types FLOAT(n, d): 4 bytes REAL(n, d): 8 bytes n means n digits total d means d digits after decimal point All (n, d) specifications are optional. FLOAT  given 1.06, displays 1.06 FLOAT(10, 1)  given 1.06, displays 1.1 FLOAT(10, 6)  given 1.06, displays

String and Date Data Types Data Types DATE: 3 bytes CHAR(n): Fixed # of characters. Allocates the specified amount of storage. VARCHAR(n): Variable characters. Stores the amount of data actually inserted, plus a two-byte length marker, with total not more than n. All (n) specifications are optional CHAR(1)  Given ‘s’, displays s CHAR(1)  Given ‘sample’, displays ‘s’ CHAR(10)  Given ‘sample’, displays ‘sample’ Prefer VARCHAR to CHAR

Data Definition Language (DDL) You can use DML and DDL commands in the console, query browser, and within an SQL script file MYSQL Workbench has a GUI tool that can generate DDL. You might use it in real life, but *do not use it for assignments in this class.* You must first learn DDL yourself! Transactions (BEGIN, ROLLBACK, and COMMIT) do not work with DDL commands.

Special Notes Do not try to memorize all these commands Use templates After a while, you’ll remember them

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

CREATE TABLE Example Example: CREATE TABLE musician(Name varchar(30));

CREATE TABLE Example CREATE TABLE can also take an optional ENGINE parameter at the end (MySQL only): CREATE TABLE Musician ( Name VARCHAR(32) NOT NULL ) Engine=InnoDB; MySQL uses pluggable storage engines Default is MyISAM Another popular one is InnoDB Currently only InnoDB enforces foreign keys Many uncommon ones are listed herehere

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;

Adding Columns Example: ALTER TABLE Musician ADD COLUMN MusicianID INT PRIMARY KEY FIRST; ALTER TABLE Musician ADD COLUMN Title VARCHAR(20) NULL; INSERT INTO Musician VALUES(1, ‘Sid’, ‘Bassist’);

Editing Columns MODIFY lets 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

Editing Columns Examples: -- Let’s rename the Title column to Instrument. ALTER TABLE Musician CHANGE Title Instrument VARCHAR(32) NOT NULL;

Dropping Columns Syntax: ALTER TABLE tablename DROP COLUMN column_name; Examples: ALTER TABLE Musician DROP COLUMN Instrument;

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: Requires data (other than the primary key) to be unique.

Primary Key Constraints CREATE TABLE Syntax: Can add the keyword PRIMARY KEY at end of column definition ALTER TABLE Syntax: ALTER TABLE tablename ADD CONSTRAINT constraint_name PRIMARY KEY (field1, field2,...);

Examples Examples: CREATE TABLE Musician( MusicianID INT NOT NULL, CONSTRAINT pk_musicianID PRIMARY KEY(MusicianID) ); CREATE TABLE Musician( MusicianID INT PRIMARY KEY ); Create table tracks(titleid int, tracknum int, primary key(titleid, tracknum));

Foreign Key Constraints Sometimes called integrity constraints CREATE TABLE Syntax: FOREIGN KEY(field1, field2,...) REFERENCES parent_table(field1, field2,...) In members:..foreign key(salesid) references salespeople (salesid)‏ ALTER TABLE Syntax: ALTER TABLE tablename ADD CONSTRAINT constraint_name FOREIGN KEY (field1, field2,...) REFERENCES parent_table(field1, field2,...);

Foreign Key Constraints Example: ALTER TABLE members ADD CONSTRAINT fk_salespeople foreign key(salesID) references salespeople(salesID); Now try this: INSERT INTO members values (1, "Anderson", "Aaron", "1 Main St", "Anytown", "ZZ", "12345", "USA", 123, " ", 500); Fails because there is no salesperson #500

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.

Unique Constraints ALTER TABLE Syntax: ALTER TABLE tablename ADD CONSTRAINT constraint_name UNIQUE (fieldname1, fieldname2); eg, ALTER TABLE musician ADD CONSTRAINT uniq UNIQUE (Instrument); Now, insert into musician values(‘Vuvuzuelist’) will work, but insert into musician values(‘Pianist’) will fail

Unique Constraints Examples: CREATE TABLE login( user_id INT PRIMARY KEY, username VARCHAR(32) NOT NULL UNIQUE, password VARCHAR(32) NOT NULL ); INSERT INTO login values (1, ‘bsmith’, mypassword’); INSERT INTO login values (2, ‘bsmith’, ‘anotherpass’);

Default Constraints Using CREATE 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;

Default Constraints Examples: DROP TABLE login; CREATE TABLE login(user_id INT NOT NULL PRIMARY KEY, username VARCHAR(32) NOT NULL UNIQUE, password VARCHAR(32) DEFAULT ‘godzilla’ NOT NULL);

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;

Examples Examples: ALTER TABLE members DROP FOREIGN KEY fk_salespeople;

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

Identity Column Example Example: DELETE FROM Musician; ALTER TABLE musician add column id int primary key AUTO_INCREMENT; INSERT INTO Musician VALUES('Guitarist', 'Keith', 0); INSERT INTO Musician VALUES('Drummer', 'Charlie', 0); What happens with INSERT INTO Musician VALUES(‘Bassist’, ‘Bill', 2) ?

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

Dropping Tables When dropping tables where foreign keys are enforced, it is useful to type in the following foreign key check commands when using the InnoDB storage engine SET FOREIGN_KEY_CHECKS = 0; DROP TABLE IF EXISTS tablename; SET FOREIGN_KEY_CHECKS = 1; Else you would have to think very carefully about how to order your deletes, since drops that would create orphans would not be executed

Scripts A script contains a series of SQL/DDL/DML commands that execute sequentially No new syntax You ran lyric.sql when you set up the Lyric DB in week one In mySQL, run from the command line with the source command, ed source test.sql

Scripts Example: drop table if exists vehicles; create table vehicles( id int not null, name varchar(30) ); insert into vehicles values(1, "Ruby"); select * from vehicles; Save as test.sql mysql> source test.sql;

Sample Problem Write DDL and DML commands to do the following: Set up a table to track information on vehicles. Include four fields: make (eg Mazda), model (eg Miata), license plate number, state of registration. Also include an autoincrement field and make it the primary key. Enter information on three real or fictional vehicles. Use the following for one of the license plate numbers: 1ABC123 Change the state of registration to MI for the vehicle with plate number 1ABC123 Alter the table to include an additional field with the color of the vehicle