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alias
You can use an alias to refer to a column in the GROUP BY
,
ORDER BY
, or in the HAVING
part. Aliases can also be used
to give columns better names:
SELECT SQRT(a*b) as rt FROM table_name GROUP BY rt HAVING rt > 0; SELECT id,COUNT(*) AS cnt FROM table_name GROUP BY id HAVING cnt > 0; SELECT id AS "Customer identity" FROM table_name; |
Note that standard SQL doesn't allow you to refer to an alias in a
WHERE
clause. This is because when the WHERE
code is
executed the column value may not yet be determined. For example, the
following query is illegal:
SELECT id,COUNT(*) AS cnt FROM table_name WHERE cnt > 0 GROUP BY id; |
The WHERE
statement is executed to determine which rows should
be included in the GROUP BY
part while HAVING
is used to
decide which rows from the result set should be used.