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Structured Query Language

Lesson 09

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History of SQL Developed by IBM

Adopted as standard language for commercialRDBMS

A comprehensive non-procedural databaselanguage package that supports standard

Supports both DDL and DML Provides facilities to specify security, authorization

(mainly through DCL), and constraints

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SQL Data Definition Commands Create Schema

Create tables

Create Domain Create view

Alter Table/Schema

Drop Table/Schema

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Data Definition Language CREATE

ALTER DROP

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Schema and Catalog SQL schema

Used to group table and related constructs i

dentified by Schema name

Contains elements such as; Tables ConstraintsViews and domainsAuthorization constructs

Catalog Named collection of schema

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Create Schema CREATE SCHEMA

[AUTHORIZATION ]

E.g. CREATE SCHEMA CompanyAUTHORIZATION

JSMITH JSMITH is Schema Owner

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Attribute Data Types and

Domains in SQL Basic Data types

Numeric

Integer, Real

Char string

Fixed length (CHAR(n))

Varying length (VARCHAR(n)

date/time

Boolean (T,F, Unknown)

User defined data type Domain in SQL

CREATE DOMAIN DEP_TYPEAS CHAR (9);

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Create Table CREATE TABLE [Schema Name]. (Attribute List)

E.g. CREATE TABLE Company.Employees

( EmpID int,FirstName varchar(20),Last Name varchar(20),

Address varchar(100))

CREATE TABLE Employees ..

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Specifying Constraints using

SQL Constraints and default values can

specified on each table, tuple, andattributes

Integrity Constraints will be in 3 forms

Domain Integrity

Entity Integrity

Referential Integrity

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Domain Integrity CHECK Constraints

NOT NULL DEFAULT Value

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Using CHECK Constraint Use CHECKfor more general constraints Used at the end of schema

Applies to individual tuples E.g.,

Supposing that DNUMBER should be between1 and 10 DNUMBER INT CHECK(DNUMBER>0AND

DNUMBER 0AND D_NUM

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Using NOT NULL

E.g.

Suppose that DNUMBER cannot be leftblank

DNUMBER INT NOT NULL CHECK(DNUMBER>0AND DNUMBER 0AND D_NUM

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Specifying Entity Integrity PRIMARY KEY CLUASE used to specify PK

E.g., PRIMARY KEY(DNUMBER);

UNIQUE CLAUSE

Used for secondary keys

NICNo varchar(20) UNIQUE

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Specifying Referential

Integrity FOREIGN KEY CLUASE used to specify

FK

FOREIGN KEY(DNUMBER) REFERENCESDEPARTMENT (DUNMBER)

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Example CREATE TABLE Employees(

EmpID Int,FirstName nvarchar(20) NOT NULL,LastName nvarchar(20),NICNo nvarchar(15) UNIQUE,DeptNo int CHECK (DeptNo>0 AND DeptNO

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SCHEMA CHANGE COMMANDS

IN SQL THE DROP COMMAND

Used to drop the named schema elementsfrom database schema

E.g.,

DROP SCHEMA COMPANYCASCADE

DROP TABLE DEPENDENT CASCADE

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The ALTER TABLE Command Used to change the definition of base table

E.g.,

ALTER TABLE COMPANY.EMPLOYEEADD JOBVARCHAR(12)

ALTER TABLE COMPANY.EMPLOYEE DROPADDRESSCASCADE;

ALTER TABLE COMPANY.DEPARTMENTALTER MGRSSNDROP DEFAULT;

ALTER TABLE COMPANY.DEPARTMENTALTER MGRSSNSET DEFAULT344556677

ALTER TABLE COMPANY.EMPLOYEE DROP CONSTRAINTEMPSUPERFKCASCADE

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Data Manipulation Language SELECT

INSERT UPDATE

DELETE

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SELECT Statement General Form:

SELECT

FROM

WHERE

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SELECT Statement SELECT *

FROM Employee

Selects all the attributes and all thetuples from Employee Table

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ORDER BY Clause SELECT *

FROM Employee

ORDER BY deptno SELECT *

FROM EmployeeORDER BY deptno, name

SELECT name, job, salary, EmpIDFROM EmployeeORDER BY salary DESC

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IN, BETWEEN and LIKE SELECT *

FROM EmployeeWHERE deptno IN (10,20,50)

SELECT *FROM EmployeeWHERE job = salaryBETWEEN 35000 AND 45000

SELECT *FROM EmployeeWHERE nameLIKE 'W%'

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Aggregate Functions SELECT AVG(salary)

FROM Employee

SELECT COUNT(*)FROM Employee

SELECT COUNT(FirstName)FROM Employee

SELECT COUNT DISTINCT(FirstName)FROM Employee

SELECT MAX(salary)FROM Employee

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JOINING Tables:

Ambiguous Attribute Names and Renaming

Need to qualify the attributes whenthey are the same

use . separator to qualify the attribute e.g.,

SELECT FNAME, EMPLOYEE.NAME, ADDRESS

FROM EMPLOYEE, DEPARTMENT

WHERE DEPARTMENT.DNUMBER =EMPLOYEE.DNUMBERAND

DEPARTMENT.NAME = Research

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Ambiguity: Recursive

relationships For each employee, find the employees first

and last name and the first and last name of

her immediate supervisor SELECT E.FNAME, E.LNAME, S.FNAME, S.LNAME

FROM EMPLOYEEAS E, EMPLOYEEAS S

WHERE E.SUPERSSN=S.SSN

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Unspecified WHERE-Clause No WHERE-clause means no

conditions

No condition means Cross productoperations

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No WHERE Clause Get all combinations of EMPLOYEE.SSN

and DEPARTMENT.DNAME

SELECT SSN, DNAME

FROM EMPLOYEE, DEPARTMENT

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Nested Queries Some queries need the existing valuesin the database to be retrieved

Nested queries used to formulate suchqueries

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Nested Query SELECT DISTINCT PNUMBER

FROM PROJECT

WHERE PNUMBER IN (SELECT PNUMBER FROM DEPARTMENT, EMPLOYEE , PROJECT

WHERE DNUM = DNUMBERAND MGRSSN = SSNAND LNAME = Smith)

OR

PNUMBER IN (SELECT PNO FROM WORKS_ON, EMPLOYEE

WHERE ESSN=SSNAND LNAME = Smith)

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Correlated nested queries Correlated Queries:

When a condition in WHERE clause of anested query references attribute(s) of arelation defined in the outer query

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Correlated query Get the name of each employee who has a

dependent with the same first name and the same

sex

as the employee SELECT E.FNAME, E.LNAME

FROM EMPLOYEEAS E

WHERE E.SSN IN (SELECT ESSN

FROM DEPENDENTWHERE E.FNAME=DEPENDENT_NAME

AND E.SEX=SEX);

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Correlated query A nested query involving = or IN can be replaced

by simple query SELECT E.FNAME,E.LNAME

FROM EMPLOYEEAS E, DEPEDENTAS D

WHERE E.SSN=D.ESSNAND E.FNAME=D.DEPENDENT_NAMEANDE.SEX=D.SEX);

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EXISTS EXISTS:

Checks the result to see if a correlated

nested query is empty or not

If the result (i.e., set) is empty it returnsfalse

If the resultis Not empty it returns true

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EXISTS Find the name of each employee who has a

dependent with the same first name and same sex asthe employee

SELECT E.FNAME, E.LNAME

FROM EMPLOYEE E

WHERE EXISTS (SELECT *

FROM DEPENDENT

WHERE E.SSN=ESSNAND SEX=E.SEXAND

E.FNAME=DEPENT_NAME)

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NOT EXISTS Find the name of each employee who

has no dependent SELECT FNAME, LNAME

FROM EMPLOYEE E

WHERE NOT EXISTS (SELECT *

FROM DEPENDENT

WHERE SSN=ESSN)

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NULL Null can be interpreted as

Unknown

Unavailable Not applicable

Retrieve the names of all employees who donot have supervisors

SELECT FNAME, LNAME

FROM EMPLOYEE

WHERE SUPERSSN IS NULL;

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Grouping and COUNT GROUP BY CLUASE

Used to partition the relation into sub-relation

Works with

aggregate functions

grouping attribute

Grouping attribute (s) need to be specify in SELECT clause

Create separate group for the grouping attribute with NULLvalues

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GROUP BY For each department, retrieve the

department number, the number of

employees in the department, and theiraverage salary

SELECT DNO, COUNT(*),AVG(SALARY)

FROM EMPLOYEE

GROUP BYDNO;

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HAVING Clause Used with GROUP BY clause

Provides a condition on the sub relations or

groups Groups satisfying the conditions are selected

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Having For each project on which more than two employees

work, retrieve the project number, the project name,the number of employees who work on the project

SELECT PNUMBER, PNAME, COUNT(*)

FROM PROJECT, WORKS_ON

WHERE PNUMBER=PNO

GROUP BYPNUMBER, PNAME

HAVING COUNT(*)>2;

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HAVING and COUNT SELECT DNUMBER, COUNT (*)

FROM DEPARTMENT, EMPLOYEE

WHERE DNUMBER=DNOANDSALARY>4000AND DNO IN (SELECT DNO FROM EMPLOYEE

GROUP BY DNO HAVING COUNT(*)>5)

GROUP BYDNNUMBER

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Insert, Delete, and Update The Insert Command

To add a new tuple to employee INSERT INTO EMPLOYEEVALUES(1, John, Smith,12/07/1980,10))

To enter a new tuple with knownattributes INSERT INTO EMPLOYEE (EmpID,

FirstName, LastName)

VALUES (3,John, Smith);

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Insert Multiple tuples INSERT command can be used to load

multiple tuples as the same time Suppose

CREAT TABLE DEPT_INFO (DEPT_NAME VARCHAR(15),

NO_OF_EMPS INTEGER,TOTAL_SAL INTEGER);

INSERT INTO DEPTS_INF (DEPT_NAME, NO_OF_EMPS,TOTAL_SAL)

SELECT DNAME, COUNT(*), SUM (SALARY)FROM (DEPARTMENT JOIN EMPLOYEE ON

DNUMBER=DNO)GROUP BY DNAME;

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The DELECT Command Removes tuples from a relation one at a

time

DELETE FROM EMPLOYEE

WHERE LNAME=Brown

Deletion can be cascaded to other relations

using referential triggered actions specifiedin schema

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DELETE One or more tuples can be deleted

E.g.. Delete all employees who work for

research dept. DELETE FROM EMPLOYEE

WHERE DNO IN

(SELECT DNUMBER

FROM DEPARTMENT

WHERE DNAME=Research);

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UPDATE Command

Used to modify values of one (or multiple)

selected tuples associated with ONE relation E.g.,

Change the location and controlling departmentnumber of project number 10 to Grand Forks and5

UPDATE PROJECT

SET PLOCATION = Grand Forks, DNUM=5

WHERE PNUMBER=10;