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Question:What is difference between Co-related sub query and nested sub query?



asked Sep 13, 2013 in Java Interview Questions by ashish singh
edited Sep 12, 2013
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Correlated subquery runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query. Nested subquery runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row. For example, Correlated Subquery: select e1.empname, e1.basicsal, e1.deptno from emp e1 where e1.basicsal = (select max(basicsal) from emp e2 where e2.deptno = e1.deptno) Nested Subquery: select empname, basicsal, deptno from emp where (deptno, basicsal) in (select deptno, max(basicsal) from emp group by deptno)
answered Sep 13, 2013 by ashish singh
edited Sep 12, 2013
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Correlated subquery runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query. Nested subquery runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row. For example, Correlated Subquery: select e1.empname, e1.basicsal, e1.deptno from emp e1 where e1.basicsal = (select max(basicsal) from emp e2 where e2.deptno = e1.deptno) Nested Subquery: select empname, basicsal, deptno from emp where (deptno, basicsal) in (select deptno, max(basicsal) from emp group by deptno)
answered Sep 13, 2013 by ashish singh
edited Sep 12, 2013

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