SQL Having Clause

The SQL GROUP BY statement is used along with the SQL aggregate functions like SUM to provide means of grouping the result data set by certain database table column(s).

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. It allows us to calculate aggregate of groups within our table.

The SQL HAVING clause is used to restrict conditionally the output of a SQL statement, by a SQL aggregate function used in your SELECT list of columns. You can't specify a fact in a SQL WHERE clause against a column in the SELECT list for which SQL aggregate function is used.

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. This clause is applied after grouping is applied. Without the HAVING keyword it would not be possible to test for function result conditions.

The syntax for the HAVING function is:

SELECT Column,

SUM(column) FROM

table GROUP BY Column

HAVING SUM (Column) condition value

SELECT Company,

SUM (Amount) FROM

Sales GROUP BY Company

HAVING SUM (Amount) > 10,000

SELECT Employee,

SUM (Hours)FROM

Employee Hours WHERE

SUM (Hours) > 24 hours GROUP BY Employee

SELECT Employee,

SUM (Hours)FROM

Employee Hours GROUP BY

Employee HAVING SUM (Hours) > 24