An alias can be used in a query select list to give a column a different name. You can use the alias in GROUP BY, ORDER BY, or HAVING clauses to refer to the column:

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:

The WHERE clause determines which rows should be included in the GROUP BY clause, but it refers to the alias of a column value that is not known until after the rows have been selected, and grouped by the GROUP BY.

In the select list of a query, a quoted column alias can be specified using identifier or string quoting characters:

Elsewhere in the statement, quoted references to the alias must use identifier quoting or the reference is treated as a string literal. For example, this statement groups by the values in column id, referenced using the alias `a`:

But this statement groups by the literal string 'a' and will not work as expected: