MySQL - 在 WHERE 中选择 AS
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MySQL - SELECT AS in WHERE
提问by Martin
For some reason, this doesn't work:
出于某种原因，这不起作用：
select substring(rating, instr(rating,',') +1, +2) as val
from users where val = '15';
It gives this error:
它给出了这个错误：
ERROR 1054 (42S22): Unknown column 'val' in 'where clause'
错误 1054 (42S22)：“where 子句”中的未知列“val”
How do I do it then?
那我该怎么做呢？
回答by John Woo
First, you cannot use ALIASon the WHEREclause. You shoul be using the column,
首先，不能使用ALIASonWHERE子句。你应该使用专栏，
SELECT SUBSTRING(rating, INSTR(rating,',') +1, +2) AS val
FROM users
WHERE SUBSTRING(rating, INSTR(rating,',') +1, +2) = '15'
The reason is as follows: the order of operation is SQL,
原因如下：操作顺序是SQL，
- FROM clause
- WHERE clause
- GROUP BY clause
- HAVING clause
- SELECT clause
- ORDER BY clause
- FROM 子句
- WHERE 子句
- GROUP BY 子句
- HAVING 子句
- SELECT 子句
- ORDER BY 子句
the ALIAStakes place on the SELECTclause which is before the WHEREclause.
theALIAS发生在该SELECT子句之前的WHERE子句上。
if you really want to use the alias, wrap it in a subquery,
如果您真的想使用别名，请将其包装在子查询中，
SELECT *
FROM
(
SELECT SUBSTRING(rating, INSTR(rating,',') +1, +2) AS val
FROM users
) s
WHERE val = '15'
回答by echo_Me
valis not defined, it's just an alias. Do it like this:
val没有定义，它只是一个别名。像这样做：
SELECT SUBSTRING(rating, INSTR(rating,',') +1, +2) AS val
FROM users
WHERE SUBSTRING(rating, INSTR(rating,',') +1, +2) = 15
回答by u10679283
You can use this query
您可以使用此查询
SELECT SUBSTRING(rating, INSTR(rating,',') +1, +2)
FROM users
WHERE SUBSTRING(rating, INSTR(rating,',') +1, +2) = '15'
