
Using the EXISTS Command in SQL
Suppose you wanted to retrieve the department number (deptno) and name (dname) fields for employees in an emp table. One way to get the values is with this SQL query: SELECT distinct d.deptno,d.dnameFROM dept d,emp eWHERE d.deptno=e.deptno The preceding query takes four milliseconds to execute (on my machine). But if