Question

我想要做的就是让我在表中的id上出现，然后根据出现的数量，将另一列的值除以该值。这是查询，以更好地说明我正在尝试做什么。

SELECT t.t_id, count(DISTINCT tm.tm_id) AS occurances, t.value/occurances AS newValue
FROM table t
INNER JOIN table_map tm ON t.t_id = tm.tm_id
GROUP BY tm.tm_id
HAVING occurances > 1

对于那些熟悉SQl的人来说，这不会起作用。然而，我不知道如何让它执行我需要的，或者如果可能的话。我尝试在select中做一个select，但是无法弄清楚如何让它来执行我需要的操作。

正在MySQL 5 DB上执行sql

Answer 1

也许你的意思是这样的：

SELECT
  t.t_id,
  t.occurrences,
  t.value / tm.occurrences AS newValue
FROM table t
  INNER JOIN (
    SELECT
      tm_id,
      COUNT(*) AS occurrences
    FROM table_map
    GROUP BY tm_id
    HAVING COUNT(*) > 1
  ) tm ON t.t_id = tm.tm_id

Answer 2

将其抛入子查询并在此之后进行数学运算：

SELECT t_id, occurances, value/occurances AS newValue
from (
    SELECT t.t_id, count(DISTINCT tm.tm_id) AS occurances, t.value
    FROM table t
    INNER JOIN table_map tm ON t.t_id = tm.tm_id
    GROUP BY t.t_id
    HAVING occurances > 1) t

在SQL中对临时列执行数学运算

2 个答案: