sql - How to work with Table joins and Inline View -

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can me understand sql query; don't understand concept behind it:

select     t2.*,     (         select sum (salary)         (             select             tb1.*,              rownum rnk             (                  select *                 employees e                 order e.department_id, e.employee_id             ) tb1         ) tb2           tb2.department_id = t2.department_id , tb2.rnk <= t2.rnk     ) dept_salary (     select            t1.*,          rownum rnk     (           select                e.employee_id,             e.first_name,             e.department_id,             e.salary         employees e         order   e.department_id, e.employee_id     ) t1 ) t2

there different type of subquery.

  1. scalar sub query : query totally independent main query.

    select empno, (select count(*) emp) total_emp emp

here subquery totally independent of main query.

  1. corelated sub query: sub query reffers main query.

    select empno, (select deptname dept d e.deptno = d.deptno) deptname emp e

  2. inline view :a sub query used table or view in sql

    select * (select empno, deptname emp e, dept d e.deptno = d.deptno) sal > 100

from query:

select     t2.*,     (         select sum (salary)  -- start corelated sub query         (             select             tb1.*,              rownum rnk             (                  select *  -- start scalar sub query                 employees e                 order e.department_id, e.employee_id -- end scalar sub query             ) tb1          ) tb2           tb2.department_id = t2.department_id , tb2.rnk <= t2.rnk -- end corelated sub query     ) dept_salary (     select   -- start inline view         t1.*,          rownum rnk     (           select                e.employee_id,             e.first_name,             e.department_id,             e.salary         employees e         order   e.department_id, e.employee_id     ) t1 ) t2  -- end inline view

nb:now can find out sub query within sub query , inline view within inline view in question.


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