SQL Function

SQL GROUP BY and HAVING

Aggregate functions (like SUM) often need an added GROUP BY functionality.

GROUP BY...

GROUP BY... was added to SQL because aggregate functions (like SUM) return the aggregate of all column values every time they are called, and without the GROUP BY function it was impossible to find the sum for each individual group of column values.

The syntax for the GROUP BY function is:

GROUP BY Example

This “Sales report" Table:

And This SQL:

Returns this result:

The above code is invalid because the column returned is not part of an aggregate. A GROUP BY clause will solve this problem:

Returns this result:

HAVING...

HAVING... was added to SQL because the WHERE keyword could not be used against aggregate functions (like SUM), and without HAVING... it would be impossible to test for result conditions.

The syntax for the HAVING function is:

This "Sales report" Table:

This SQL:

Returns this result