Structured Query Language

Brief History Developed in early 1970 for relational data model: –Structured English Query Language (SEQUEL) –Implemented with IBM System R 1987 first ISO standard version 1992 SQL SQL 3 –Object-relational model 2003:SQL 2003 –SQL/XML Products: DB2, Oracle, MS SQL, MySQL

Language Overview Three major components: –Data definition language Create Table –Data manipulation language Updating database: –Insert, Delete, Update Query database: –Select –Data control language (DCL) Help DBA control the database: –Grant/revoke privileges to access the database, creating procedures, etc. Interface with database: –Entering command interactively at the DBMS command prompt. –Embedded in a procedural language

Data Definition Language SQL Identifiers –Character set: A-Z, a-z, 0-9, _ –<= 128 characters –Start with a letter –Cannot contain spaces

SQL Data Types Boolean –True, False, Unknown (for Null) Character –Fixed length: CHARACTER(n), CHAR(n), CHAR – default to 1 character –Varying length: CHARACTER VARYING(n): Maximum length is n VARCHAR(n) Numeric –NUMERIC(i,j), DECIMAL(i,j), DEC(i,j) –INTEGER, INT, SMALLINT – up to –FLOAT, REAL, DOUBLE PRECISION Date: –DATE –TIME –TIMESTAMP Large objects: –CHARACTER LARGE OBJECT –BINARY LARGE OBJECT

CREATE TABLE CREATE TABLE tableName(fields and data type separated by commas); Ex. –CREATE TABLE employee( eid CHAR(5), ename VARCHAR(40), sex CHAR, salary NUMERIC(9,2), hire_Date DATE);

Integrity Enhancement Feature Required data: NOT NULL –eid CHAR(5) NOT NULL, Default value:DEFAULT sex CHAR DEFAULT ‘M’, Field domain: CHECK(condition) –salary NUMERIC(9,2) CHECK (salary >= 100 AND salary <=10000), –sex CHAR DEFAULT ‘M’ CHECK (sex in (‘M’,’F”)), PRIMARY KEY –PRIMARY KEY(sid) –PRIMARY KEY(sid, cid) Unique – allow null value, the PRIMARY KEY constraint does not allow null. –ESSN CHAR(9) UNIQUE

–CREATE TABLE employee( eid CHAR(5) PRMARY KEY, ename VARCHAR(40), sex CHAR DEFAULT ‘M’ CHECK (sex in (‘M’,’F”)), salary NUMERIC(9,2), hire_Date DATE);

Composite Key Example create table orderdetail (oid char(3), cid char(5), qty numeric(5,2), primary key (oid,cid));

ALTER TABLE ADD/Modify/DROP COLUMN a new field from a table. Ex. ALTER TABLE employee ADD phone CHAR(8); ALTER TABLE employee Modify phone CHAR(9); ALTER TABLE employee DROP COLUMN Phone;

Adding Constraints with the ALTER TABLE command Constraints: –PRIMARY KEY, CHECK, UNIQUE PRIMARY KEY: –ALTER TABLE tablename –ADD CONSTRAINT constraintname –PRIMARY KEY (columnname); CHECK –ALTER TABLE tablename –ADD CONSTRAINT constraintname –CHECK (criteria);

Examples ALTER TABLE emp ADD CONSTRAINT empkey PRIMARY KEY (empid); ALTER TABLE emp ADD CONSTRAINT validSalary CHECK (salary between 100 AND 20000); Note: Constraints information are stored in table: USER_CONSTRAINTS. You can use the DESCRIBE command to show fields in this table.

Dropping Constraints ALTER TABLE tablename DROP CONSTRAINT constraintname;

Disable/Enable Constraints ALTER TABLE tablename DISABLE CONSTRAINT constraintname; ALTER TABLE tablename ENABLE CONSTRAINT constraintname;

Creating Table Through SubQuery CREATE TABLE tableName AS (Select query) Ex. –CREATE TABLE newEmp –AS (SELECT empid, ename,salary FROM emp);

Renaming a Table Rename oldName to newName

Removing a Table DROP TABLE tableName

SQL Insert Command INSERT INTO tableName VALUES (field values separated by commas); INSERT INTO tableName (Column names separated by commas)VALUES (field values separated by commas); Ex 1. Customer table with CID, CNAME, CITY, RATING. a. INSERT INTO CUSTOMER VALUES (‘C1’, ‘SMITH’, ‘SF’, ‘A’); b. INSERT INTO CUSTOMER (CID, CNAME,RATING) VALUES (‘C1’, ‘SMITH’, ‘A’);

Record with Date Field Oracle date format: –‘dd-mmm-yyyy’ Example: insert into orders values('O7','c2','s1','10-oct-2007');

Inserting records from an existing table INSERT INTO stu2 (select * from student);

SQL Delete Command DELETE FROM tableName [WHERE criteria]; Ex 1. Delete a record from the Customer table. DELETE FROM CUSTOMER WHERE CID = ‘C1’;

SQL Update Command UPDATE tableName SET field = new value [WHERE criteria]; Ex 1. UPDATE CUSTOMER SET RATING = ‘A’ WHERE CID=‘C1’; Ex 2. UPDATE CUSTOMER SET CITY = ‘SF’, RATING = ‘A’ WHERE CID=‘C1’;

Dealing with Null Null is a key word. We can use Null in the INSERT, UPDATE, and DELETE command. Use IS NULL (or IS NOT NULL) in a criteria. Examples: –INSERT INTO emp VALUES (‘e95’,’June’,’f’,NULL,5000); –UPDATE emp SET salary=null where empid=‘e99’; –SELECT * FROM emp WHERE salary IS NULL; –SELECT * FROM emp WHERE salary= NULL (not working);