3.8 WHERE Clauses and Column Aliases
3.8.1 Problem
You want to refer to a
column alias in a WHERE clause.
3.8.2 Solution
Sorry, you cannot.
3.8.3 Discussion
You cannot refer to column aliases in a WHERE
clause. Thus, the following query is illegal:
mysql> SELECT t, srcuser, dstuser, size/1024 AS kilobytes
-> FROM mail WHERE kilobytes > 500;
ERROR 1054 at line 1: Unknown column 'kilobytes' in 'where clause'
The error occurs because aliases name output
columns, whereas a WHERE clause operates on
input columns to determine which rows to select
for output. To make the query legal, replace the alias in the
WHERE clause with the column or expression that
the alias represents:
mysql> SELECT t, srcuser, dstuser, size/1024 AS kilobytes
-> FROM mail WHERE size/1024 > 500;
+---------------------+---------+---------+-----------+
| t | srcuser | dstuser | kilobytes |
+---------------------+---------+---------+-----------+
| 2001-05-14 17:03:01 | tricia | phil | 2338.36 |
| 2001-05-15 10:25:52 | gene | tricia | 975.13 |
+---------------------+---------+---------+-----------+
|
