Using column alias in WHERE clause of MySQL query produces an error

Question

The query I\'m running is as follows, however I\'m getting this error:

#1054 - Unknown column \'guaranteed_postcode\' in \'IN/ALL/ANY subquery\'

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Answer 1

You can use HAVING clause for filter calculated in SELECT fields and aliases

Answer 2

Standard SQL disallows references to column aliases in a WHERE clause. This restriction is imposed because when the WHERE clause is evaluated, the column value may not yet have been determined. For example, the following query is illegal:

SELECT id, COUNT(*) AS cnt FROM tbl_name WHERE cnt > 0 GROUP BY id;