Introduction To SQL Lynnwood Brown President System Managers LLC Copyright System Managers LLC 2003 all rights reserved

Introduction To SQL

Lynnwood Brown

President System Managers LLC

Copyright System Managers LLC 2003 all rights reserved.

Structured Query Language

• The Structured Query Language is used to communicate with all relational databases.

• Oracle, DB2, Informix, SQL Server, MS Access are some of the more popular databases.

Oracle - 30% market share

DB2 - 30% market share

SQL Server - 15% market share


Getting Information

• A database consist of various types of objects.

• One type of database object is called a table.

• Tables store end user information in records.


Getting Information

• End users must be able to insert new data into a table.

• End users must be able to update the information in a table.

• End users must be able to remove information from a table.

• End users must be able to look up information that is stored in a table.


Getting Information

• To get information from a table the table is queried.

• To get information from a table the SQL command “SELECT” is used to query the table.


Getting Information

• To find the name, locations and department numbers from the table called “DEPT” a “SELECT” statement is issued.

• Select deptno,dname,loc from dept;


Getting Information

• SQL supports the use of functions to aggregate data.

• Partial list of SQL functions:MIN - Find the minimum value in a column

MAX - Find the maximum value in a column

AVG - Calculate the average value for a column

SQRT - Calculate the square root for the column data

STDDEV - Calculate the standard deviation for a column.

TO_CHAR - Convert data to character format


Getting information

• SQL supports a conditional search using the “WHERE” clause.

• Select * from dept where deptno = 10;

• Select * from dept where loc = ‘DALLAS’;


Getting Information

• Data may be stored in various tables.

• Data form multiple tables can be queried using a table join.

• Tables are joined on like columns.

Select a.ename,b.loc from emp a, dept b where a.deptno=b.deptno;

Select a.ename, b.loc from emp a, dept b where a.deptno > b.deptno;


Getting Information

• We can use one query as a input for another query. This is called a subquery.

Select * from emp where deptno = select deptno from dept where loc = ‘DALLAS’;

Select * from emp where deptno in (select deptno from dept);

Select * from emp where deptno in (select deptno from dept where loc in (‘DALLAS’,’BOSTON’);


Creating A Table

• The SQL command “CREATE TABLE” is used create a table.

CREATE TABLE EMP (EMPNO NUMBER(4) NOT

NULL,ENAME VARCHAR2(10),JOB VARCHAR2(9),MGR NUMBER(4),HIREDATE DATE,SAL NUMBER(7,2),COMM NUMBER(7,2),DEPTNO NUMBER(2));


Modifying A Table

• Columns can be added to an existing table using the SQL command “ALTER TABLE”.

Alter table emp add loc varchar2(20);

• Columns can be enlarged using the “ALTER TABLE” command.

Alter table emp modify loc varchar2(40);

• Columns can be removed from a tableAlter table emp drop loc;


Adding New Information

• The SQL command “INSERT” is used to add new records to a table.

INSERT INTO EMP VALUES

(7369,'SMITH','CLERK',7902,'17-DEC-80',800,NULL,20);


Updating Information

• The SQL command “UPDATE” is used to modify data that exist in a table record.

update emp set deptno = 5;

update emp set deptno = 5 where ename = ‘SMITH’;


Removing Information

• The SQL command “DELETE” is used to remove a record(s) from a table.

Delete from emp;

Truncate table emp;

Delete from emp where ename = ‘SMITH’;


Removing A Table

• The SQL command “DROP TABLE” is used to remove a table from the database.

Drop table emp;

• Tables can also be renamed:

rename emp to emp_old;


Summary

• SQL is the language used to communicate with a relational database

• SQL provides the commands “SELECT”, “INSERT”, “UPDATE” and “DELETE” to query the database, put new information into the database, update existing data that is in the database and remove data from the database respectively.


Summary (cont.)

• SQL provides various mathematical functions (MIN, MAX, STDDEV etc…).

• The command “ALTER TABLE” is used to modify the structure of a table.

• SQL*PLUS is Oracle’s version of ANSI SQL.


Documents

Introduction To SQL Lynnwood Brown President System Managers LLC Copyright System Managers LLC 2003 all rights reserved