[英]How to use an aliased column in a MySQL WHERE clause?
我有一个这样的MySQL查询:
SELECT *, SUM(...some SQL removed for brevety) AS Occurrences FROM some_table AS q
WHERE criterion="value" GROUP BY q.P_id ORDER BY Occurrences DESC LIMIT 10;
我想将结果限制为出现次数> 0的行。 这对我来说似乎很简单,但是我似乎无法使其正常工作。 无论我在哪里尝试,无论在哪里尝试,无论何时尝试添加此限制,都不会得到任何回报。 我很肯定表中应该返回数据。 有谁知道我该怎么做?
我已经尝试过了,但是仍然无法正常工作。 有什么想法为什么它仍然不起作用?
SELECT *, SUM(...some SQL removed for brevety) AS Occurrences FROM some_table AS q
WHERE criterion="value" HAVING SUM(...some SQL removed for brevety)>0 GROUP BY q.P_id ORDER BY Occurrences DESC LIMIT 10;
我对MySQL的了解不如对SQL Server的熟悉,但是在T-SQL中,您不能在GROUP BY子句中使用别名(我本来也以为ORDER BY子句,但是自那以后就证明它是不正确的) 。 在这种情况下,您要根据GROUP BY的结果进行过滤,因此我将使用HAVING子句,如下所示:
SELECT *, SUM(... some SQL removed for brevity ...) AS Occurrences
FROM
some_table AS q
WHERE
criterion = 'value'
GROUP BY
q.P_id
HAVING
SUM(... some SQL removed for brevity ...) > 0
ORDER BY
Occurrences DESC
LIMIT 10;
这个查询对我有用...
select order_id, sum(qty_ordered) as total_qty
from sales_flat_order_item
group by order_id
having total_qty > 10
order by total_qty desc
啊,我找到了它的地方。
现在的声明是:
SELECT *, SUM(...some SQL removed for brevety) AS Occurrences FROM some_table AS q
WHERE criterion="value" GROUP BY q.P_id HAVING SUM(...some SQL removed for brevety)>0 ORDER BY Occurrences DESC LIMIT 10;
似乎可以通过ORDER BY Occurrences正常工作,
根据SQL标准,列的别名在查询正文中不可用,这是一个令人烦恼的麻烦。 给定您尝试过的内容,听起来好像MySQL(和其他一些DBMS)也是如此。 您可能必须在ORDER BY子句中重复该表达式。
另外,GROUP BY子句应列出*中的每一列,而不仅仅是主键(尽管从逻辑上讲,指定主键就足够了)。
我认为聚合应该在HAVING
子句中。 虽然,我当然不知道是否接受别名。
HAVING (Occurrences > 0)
HAVING (SUM(...some SQL removed for brevety) > 0)
或者,您可以使用子查询:
SELECT *
FROM (
-- your current query
) AS sub
WHERE (Occurences > 0)
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