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mysqlsqlhavinghaving-clause

Can you use an alias in the WHERE clause in mysql?

I need to use an alias in the WHERE clause, but It keeps telling me that its an unknown column. Is there any way to get around this issue? I need to select records that have a rating higher than x. Rating is calculated as the following alias:

sum(reviews.rev_rating)/count(reviews.rev_id) as avg_rating
Solution

  • You could use a HAVING clause, which can see the aliases, e.g.

     HAVING avg_rating>5

    but in a where clause you'll need to repeat your expression, e.g. 

     WHERE (sum(reviews.rev_rating)/count(reviews.rev_id))>5

    BUT! Not all expressions will be allowed - using an aggregating function like SUM will not work, in which case you'll need to use a HAVING clause.

    From the MySQL Manual:

    It is not allowable to refer to a column alias in a WHERE clause, because the column value might not yet be determined when the WHERE clause is executed. See Section B.1.5.4, “Problems with Column Aliases”.