What are co related sub queries?

Answer 1

The main differencre between subquery and co-related subquery is that in subquery child query is executed first n then parent,but in co-related subquery main query is executed first(even though parenthesis are present) and then child query. Example of co-related subquery select dname from dept where exists

(select deptno from emp

where dept.deptno=emp.deptno); select dname from dept where not exists

(select deptno from emp

where dept.deptno=emp.deptno);