Select Using subqueries

Select uses a subquery Select to use a subquery that executes multiple times, as determined by the number of records. Low efficiency, not recommended. Query department number, salary greater than or equal to 2000 people,//salary less than 2000 people select distinct Deptno, (select COUNT (*) from EMP where sal>=2000 and DEP Tno=e.deptno) Great, (select COUNT (*) from EMP where sal<2000 and Deptno=e.deptno) less from EMP e where deptno  is not null; Tip: Focus on the use of sub-queries in the From,where,having section. The Select section is inefficient and is not recommended for use.

Select Using subqueries