FROM Clause in SQL with Proper Explanation

FROM clause in SQL with Proper Explanation

Table 1:-  XX_EMP  A

select * from XX_EMP A

            

EMPNO	ENAME	JOB	MGR	HIREDATE	SAL	COMM	DEPTNO
7369	Sunil	CLERK	7902	17-Dec-80	800		20
7499	Anil	SALESMAN	7698	20-Feb-81	1600	300	30
7521	Sanjay	SALESMAN	7698	22-Feb-81	1250	500	30
7566	Jai Prakas	MANAGER	7839	02-Apr-81	2975		20
7654	Manoj	SALESMAN	7698	28-Sep-81	1250	1400	30
7698	Bal Kishan	MANAGER	7839	01-May-81	2850		30
7782	Anmol	MANAGER	7839	09-Jun-81	2450		10
7788	Sushil	ANALYST	7566	09-Dec-82	3000		20
7839	Kishan	PRESIDENT		17-Nov-81	5000		10
7844	Tarun	SALESMAN	7698	08-Sep-81	1500	0	30
7876	Amit	CLERK	7788	12-Jan-83	1100		20
7900	Jai	CLERK	7698	03-Dec-81	950		30
7902	Faiz	ANALYST	7566	03-Dec-81	3000		20
7934	Vinod	CLERK	7782	23-Jan-82	1300		10

Table 2:-  XX_DEPT B

select * from XX_DEPT B

DEPTNO	DNAME	LOC
10	ACCOUNTING	NEW YORK
20	RESEARCH	DALLAS
30	SALES	CHICAGO
40	OPERATIONS	BOSTON

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

-- TABLE

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

select * from XX_EMP A, XX_DEPT B

where A.DEPTNO = B.DEPTNO  

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

-- View

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

select * from XX_EMP

select * from XX_DEPT

CREATE OR REPLACE VIEW XX_DEPT_V AS

select DEPTNO DEPARTMENT_NO, DNAME NAME , LOC LOCATION , 'IN' COUNTY from XX_DEPT

select * from XX_DEPT_V

select * from XX_EMP , XX_DEPT_V

WHERE DEPTNO = DEPARTMENT_NO

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

-- Inline View

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

select * from XX_EMP A, ( select DEPTNO DEPARTMENT_NO, DNAME NAME , LOC LOCATION , 'IN' COUNTY from XX_DEPT ) B

WHERE DEPTNO = DEPARTMENT_NO