Using the EXISTS Command in SQL

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 you write the query like this instead…

SELECT d.deptno,d.dnameFROM dept dWHERE EXISTS(select e.deptnoFROM emp eWHERE d.deptno=e.deptno);

…you’ll find that the query is much faster (about one millisecond on my machine).

Apparently, using the EXISTS command improves the performance considerably.

See also  Does It Make Sense to Splurge on a Laptop?

About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

About Our Journalist