What is SQL? Why we use SQL? SQL Process?

SQL

SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in relational database.

SQL Queries

1.     To fetch ALTERNATE records from a table. (EVEN NUMBERED)
select * from emp where rowid in (select decode(mod(rownum,2),0,rowid, null) from emp);

2.     To select ALTERNATE records from a table. (ODD NUMBERED)
select * from emp where rowid in (select decode(mod(rownum,2),0,null ,rowid) from emp);

3.     Find the 3rd MAX salary in the emp table.
select distinct sal from emp e1 where 3 = (select count(distinct sal) from emp e2 where e1.sal <= e2.sal);

4.     Find the 3rd MIN salary in the emp table.
select distinct sal from emp e1 where 3 = (select count(distinct sal) from emp e2where e1.sal >= e2.sal);

5.     Select FIRST n records from a table.
select * from emp where rownum<= &n;

Free Download SQL The Complete Reference 3rd Edition

Title : SQL The Complete Reference

Author(s) : James R Groff, Paul N. Weinberg, Andy Oppel

Edition : 3rd Edition