SubQuery in Qracle SQL

SubQuery in Qracle SQL

--=================== TABLE STRUCTURE =======================

XXSD_EMP_TL

EMPNO	ENAME	JOB	MGR	SAL	COMM	DEPTNO
7369	SMITH	CLERK	7902	800	80	20
7499	ALLEN	SALESMAN	7698	1600	300	30
7521	WARD	SALESMAN	7698	1250	500	30
7566	JONES	MANAGER	7839	2975	1200	20
7654	MARTIN	SALESMAN	7698	1250	1400	30
7698	BLAKE	MANAGER	7839	2850	1100	30
7782	CLARK	MANAGER	7839	2450	900	10
7788	SCOTT	ANALYST	7566	3000	750	20
7839	KING	PRESIDENT		5000	2000	10
7844	TURNER	SALESMAN	7698	1500	300	30
7876	ADAMS	CLERK	7788	1100	220	20
7900	JAMES	CLERK	7698	950	110	30
7902	FORD	ANALYST	7566	3000	700	20
7934	MILLER	CLERK	7782	1300	720	10

XXSD_DEPT_TL

DEPTNO	DNAME	LOC	DEPT_YEAR
10	ACCOUNTING	NEW YORK	2020
20	RESEARCH	DALLAS	2019
30	SALES	CHICAGO	2018
40	OPERATIONS	BOSTON	2017

XXSD_SAL_INFO_TL

YEAR_NAME	SAL_GRADE
2015	1000
2016	1500
2017	2000
2018	2200
2019	2500
2020	3000

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

--Single Row Sub Query   use with  "="  Operator

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

  

--WHERE--

select DEPTNO from XXSD_DEPT_TL  WHERE  DNAME in ( 'RESEARCH')

select * from XXSD_EMP_TL

WHERE DEPTNO =  ( )

select * from XXSD_EMP_TL

where DEPTNO = ( select DEPTNO from XXSD_DEPT_TL  WHERE  DNAME in ( 'RESEARCH')  ) 

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

--Multi  Row Sub Query use with "IN" Operator

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

select DEPTNO, DNAME, LOC from XXSD_DEPT_TL A

where DEPTNO IN  ( select DEPTNO from XXSD_EMP_TL where JOB = 'SALESMAN')

 select DEPTNO from XXSD_EMP_TL where JOB = 'SALESMAN'

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

--Order of Execution of Sub Query   (Last Inner to First Outer Query)

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

select *

from XXSD_EMP_TL

WHERE DEPTNO = (

                            select DEPTNO

                            from XXSD_DEPT_TL

                            where DEPT_YEAR = (

                                                            SELECT YEAR_NAME

                                                            FROM XXSD_SAL_INFO_TL

                                                            WHERE SAL_GRADE = 3000

                                                            )

                             )

EMPNO	ENAME	JOB	MGR	HIREDATE	SAL	COMM	DEPTNO
7782	CLARK	MANAGER	7839	09-Jun-81	2450	900	10
7839	KING	PRESIDENT		17-Nov-81	5000	2000	10
7934	MILLER	CLERK	7782	23-Jan-82	1300	720	10