Difference between Where and Having clauses

Monday, 1 October 2012

Difference between Where and Having clauses

The WHERE clause selects rows before grouping. The HAVING clause selects rows after grouping.
The WHERE clause cannot contain aggregate functions. The HAVING clause can contain aggregate functions.

A HAVING clause is like a WHERE clause, but applies only to groups as a whole, whereas the WHERE clause applies to individual rows. A query can contain both a WHERE clause and a HAVING clause. The WHERE clause is applied first to the individual rows in the tables . Only the rows that meet the conditions in the WHERE clause are grouped. The HAVING clause is then applied to the rows in the result set.

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