MySQL's WHERE Clause and Column Alias Limitations

Using column aliases in MySQL's WHERE clause often leads to the error "#1054 - Unknown column in 'IN/ALL/ANY subquery'". This article explains why and offers alternative approaches.

MySQL requires column names in WHERE clauses to be either directly from the table's structure or derived via dot notation. Column aliases, temporary names assigned during query processing, are not recognized.

The MySQL documentation explicitly forbids this. The reason is query execution order: the WHERE clause is evaluated before aliases are assigned. Therefore, using an alias in the WHERE clause results in undefined behavior.

To overcome this, employ the HAVING clause. This clause is designed for filtering rows after grouping and aggregation, making it appropriate when filtering on calculated columns (like those created with aliases). In situations where an alias is needed for filtering, using the alias in the HAVING clause provides a viable workaround.