sql - 计算 CASE 子句中的条件

Question

我试图根据错误代码的计数及其在特定时间段内从 SQL 查询中出现的次数获取条件值，但我编写的此查询返回所有记录的第一个满足的条件。

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

所需输出(更改计数条件以查看所需输出) COUNT

        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

您正在为表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')

... 对于表中的每一行，每次都会计算为 8；因此，无论该行中实际存在的错误代码如何，案例的第一个分支将始终匹配，因此您会在每一行看到RED。

重复子查询的效率很低，即使您将其关联起来也是如此。 Oracle 会优化/缓存它，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 case 的输入，以转换为颜色代码:

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得出您显示的结果的。你的水桶排除了很多可能性；例如，您可能希望第一个条件只是 > 5 。您完全忽略了您期望看到的 50005。如果您的基本逻辑是任何代码集都使用 2 天计数，而 null 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        

这仍然不是您预期的结果，但必须这样做，直到逻辑(和我的错误)被解释，或者您的结果被改变......