Question

我想在下面的select查询返回的COUNT_A上运行CASE语句或IF，并设置变量A_VAL的值。

SELECT A_DATE, COUNT(A_INS_NAM) AS COUNT_A
FROM TABLE1
WHERE A_INS_NAM IN
(
    SELECT A_INS_NAM FROM IWD
    WHERE I_ID IN
    (
        SELECT IM_ID FROM TIM WHERE IM_ID = (
            SELECT T_ID FROM TWS WHERE TN = 'abced')
    )
) AND A_DATE BETWEEN '2014-01-01' AND '2015-05-01' AND A_INS_NAM NOT LIKE '%pk%'

我希望输出有2列，即A_DATE，A_VAL。 A_VAL的值基于

设置

If COUNT_A  = 10, then  A_VAL = 1
If COUNT_A  = 20, then  A_VAL = 2
If COUNT_A  between 30 & 50, then  A_VAL =  3
If COUNT_A  > 50, then  A_VAL = 5

我能得到别人的帮助吗？

Answer 1

您应该使用联接而不是子查询以获得更好的性能，如下所示，您也使用聚合函数而不提供分组条件，因此它将作为单行产生，我在下面的查询中添加了GROUP BY t.A_DATE

SELECT 
  t.A_DATE,
  CASE
   WHEN COUNT(t.A_INS_NAM) = 10 THEN   1
   WHEN COUNT(t.A_INS_NAM) = 20 THEN   2
   WHEN COUNT(t.A_INS_NAM) BETWEEN 30 AND 50 THEN  3
   WHEN COUNT(t.A_INS_NAM)  > 50 THEN  5
   ELSE 'some value' 
  END AS A_VAL
FROM
  TABLE1 t
  JOIN IWD t1 ON(t.A_INS_NAM = t1.A_INS_NAM)
  JOIN TIM t2 ON(t1.IWD = t2.IM_ID)
  JOIN TWS t3 ON(t2.IM_ID = t3.T_ID )
WHERE t3.TN = 'abced'
  AND t.A_DATE BETWEEN '2014-01-01' AND '2015-05-01' 
  AND t.A_INS_NAM NOT LIKE '%pk%' 
GROUP BY  t.A_DATE

MYSQL CASE / IF超过使用SELECT选择的值

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