CASE 子句中的计数条件

Question

我正在尝试根据 SQL 查询中错误代码的计数及其在特定时间段内的出现次数获取条件值，但是我编写的这个查询 returns 第一个满足的条件对于所有记录。

我做错了什么

SELECT ERROR_CODE,
       CASE
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                      AND ERROR_CODE = '50001') > 50 THEN 'RED'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                      AND ERROR_CODE = '50001') < 50 THEN 'GREEN'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 1)
                      AND ERROR_CODE IS NULL) > 100 THEN 'RED'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 1)
                      AND ERROR_CODE IS NULL) < 100 THEN 'GREEN'
       END AS ALERT_COLOR
FROM   ERROR_LOG
GROUP  BY ERROR_CODE

样本数据

50005   05-JAN-15 11.05.51.570000000 AM
50001   05-JAN-15 02.39.57.840000000 PM
50001   05-JAN-15 02.31.06.700000000 PM
50001   05-JAN-15 02.21.49.350000000 PM
50001   05-JAN-15 01.59.13.910000000 PM
50001   05-JAN-15 01.50.05.900000000 PM
50001   05-JAN-15 01.30.19.270000000 PM
50001   05-JAN-15 01.11.10.510000000 PM
50001   05-JAN-15 12.00.00.720000000 PM
        05-JAN-15 09.42.10.670000000 AM
        05-JAN-15 09.37.31.590000000 AM

DESIRED OUPUT（更改计数条件以查看所需输出）计数

        2
 50001  8
 50005  1

SQL

SELECT ERROR_CODE,
       CASE
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                      AND ERROR_CODE = '50001') between 5 and 100 THEN 'RED'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                      AND ERROR_CODE = '50001') < 5 THEN 'GREEN'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 1)
                      AND ERROR_CODE IS NULL) > 100 THEN 'RED'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 1)
                      AND ERROR_CODE IS NULL) between 5 and 100 THEN 'GREEN'
       END AS ALERT_COLOR
FROM   ERROR_LOG
GROUP  BY ERROR_CODE

结果

Error_code   Alert_color
             GREEN
50005        ''
50001        RED

Answer 1

case Returns 计算结果为 TRUE 的第一个 input_expression = when_expression 的 result_expression。试试这个。

SELECT ERROR_CODE,
       CASE
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                      AND ERROR_CODE = '50001') between 50 and 100 THEN 'RED'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                      AND ERROR_CODE = '50001') < 50 THEN 'GREEN'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 1)
                      AND ERROR_CODE IS NULL) > 100 THEN 'RED'
         WHEN (SELECT Count(ERROR_CODE)
               FROM   ERROR_LOG
               WHERE  CRET_DTIM > Trunc(SYSDATE - 1)
                      AND ERROR_CODE IS NULL) between 50 and 100 THEN 'GREEN'
       END AS ALERT_COLOR
FROM   ERROR_LOG
GROUP  BY ERROR_CODE

Answer 2

您正在为 table 中的每一行重复每个 when 子句中的子查询，没有相关性。子查询：

          (SELECT Count(ERROR_CODE)
           FROM   ERROR_LOG
           WHERE  CRET_DTIM > Trunc(SYSDATE - 2)
                  AND ERROR_CODE = '50001')

... 每次都会对 table 中的每一行求值为 8；因此，无论该行中实际的错误代码如何，案例的第一个分支将始终匹配，因此您会看到每一行的 RED。

重复子查询效率低下，即使您关联了它。 Oracle 会 optimise/cache 它，但仍然......最好生成一次计数：

select error_code,
  count(case when cret_dtim > trunc(sysdate - 2) then 1 end) as cnt_2_day,
  count(case when cret_dtim > trunc(sysdate - 1) then 1 end) as cnt_1_day
from error_log
where cret_dtim > trunc(sysdate - 2)
group by error_code
order by error_code nulls first;

ERROR_CODE CNT_2_DAY  CNT_1_DAY
---------- --------- ----------
(null)             2          2 
50001              8          8 
50005              1          1

您的所有样本数据都不到一天，因此计数相同；如果您有两天前的数据，它们会有所不同。

然后您可以将其用作内部查询（或 CTE，如果您愿意）并将结果用作另一级别 case 的输入以转换为您的颜色代码：

select error_code,
  case
    when error_code = '50001' and cnt_1_day between 5 and 100 then 'RED'
    when error_code = '50001' and cnt_2_day < 5 then 'GREEN'
    when error_code is null and cnt_1_day > 100 then 'RED'
    when error_code is null and cnt_1_day between 5 and 100 then 'GREEN'
    else null
  end as alert_colour
from 
(
  select error_code,
    count(case when cret_dtim > trunc(sysdate - 2) then 1 end) as cnt_2_day,
    count(case when cret_dtim > trunc(sysdate - 1) then 1 end) as cnt_1_day
  from error_log
  where cret_dtim > trunc(sysdate - 2)
  group by error_code
)
order by error_code nulls first;

ERROR_CODE ALERT_COLOUR
---------- ------------
(null)     (null)       
50001      RED          
50005      (null)

这与您所说的预期结果不符，但正如我在评论中所说，我不确定您是如何从数字中得出所显示的结果的。你的桶排除了很多可能性；例如，您可能希望第一个条件只是 > 5。您完全忽略了您希望看到的 50005。如果您的基本逻辑是任何代码集使用 2 天计数而空值使用 1 天计数——这是一个飞跃——那么您可以将其概括为：

select error_code,
  case
    when error_code is not null and cnt_not_null between 5 and 100 then 'RED'
    when error_code is not null and cnt_not_null < 5 then 'GREEN'
    when error_code is null and cnt_null > 100 then 'RED'
    when error_code is null and cnt_null between 5 and 100 then 'GREEN'
    else null
  end as alert_colour
from (
  select error_code,
    count(case when cret_dtim > trunc(sysdate - 2)
      and error_code is not null then 1 end) as cnt_not_null,
    count(case when cret_dtim > trunc(sysdate - 1)
      and error_code is null then 1 end) as cnt_null
  from error_log
  where cret_dtim > trunc(sysdate - 2)
  group by error_code
)
order by error_code nulls first;

ERROR_CODE ALERT_COLOUR
---------- ------------
(null)     (null)       
50001      RED          
50005      GREEN

这仍然不是您的预期结果，但在解释逻辑（和我的错误）或更改您的结果之前必须这样做...

CASE 子句中的计数条件

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case-statement