How to use SELECT Command in SQL

How to use Select in SQL

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-- 1.  simple select :- to show table data.

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desc XX_EMP

select * from XX_EMP

select EMPNO, ENAME, DEPTNO, SAL  from XX_EMP

desc XX_DEPT

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--2. cartesian product , Table Alise   

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select * from XX_EMP A, XX_DEPT B

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--3.   Relation or join to skip Cartesian product

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no of table n = 2

actual no of joins:- (n-1) = 2-1 = 1

select *

from XX_EMP A, XX_DEPT B

where A.DEPTNO = B.DEPTNO

--====================================================

--4. Column  AS

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select EMPNO||' - '||ENAME AS "Imployee_Info"

from XX_EMP A, XX_DEPT B

where A.DEPTNO = B.DEPTNO

select A.EMPNO, A.ENAME, B.* from XX_EMP A, XX_DEPT B

where A.DEPTNO = B.DEPTNO

--====================================================

--5.  Show row number

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select ROWNUM S_No , A.* from XX_EMP A

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--6.  count(*) show total no of records

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select COUNT(*) AS "No of Records" from XX_EMP

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--7.  arithmatic opertaion in select

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select EMPNO , ENAME,  sal, (( sal *10)/100) AS "Employee Convenience"

from XX_EMP A, XX_DEPT B

where A.DEPTNO = B.DEPTNO

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--8.  Distinct  function use

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select Distinct DEPTNO  from XX_EMP

select Distinct DEPTNO  from XX_DEPT

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--9.  Same Column name use only Once Ex:- DEPTNO 

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select * from XX_EMP A, XX_DEPT B

where A.DEPTNO = B.DEPTNO