字段上的条件计数

Question

如果我有这样一张桌子:

jobId, jobName, Priority

其中,优先级可以是1到5之间的整数.

由于我需要此查询来生成报表上的图表,因此我需要显示jobid,jobname和名为Priority1,Priority2,Priority3,Priority4的5个字段.Priority5.

Priority1应计算优先级字段值为1的行数.

Priority2应计算优先级字段值为2的行数.

Priority3应计算优先级字段值为3的行数.

等等

我怎么能以快速和高效的方式做到这一点？

非常感谢,Kave

Answer 1

我想你可能会追随

select 
    jobID, JobName,
    sum(case when Priority = 1 then 1 else 0 end) as priority1,
    sum(case when Priority = 2 then 1 else 0 end) as priority2,
    sum(case when Priority = 3 then 1 else 0 end) as priority3,
    sum(case when Priority = 4 then 1 else 0 end) as priority4,
    sum(case when Priority = 5 then 1 else 0 end) as priority5
from
    Jobs
group by 
    jobID, JobName

但是我不确定你是否需要在结果中使用jobID和JobName,如果这样删除它们并删除组,

Answer 2

使用COUNT而不是SUM将删除对ELSE语句的要求:

SELECT jobId, jobName,
    COUNT(CASE WHEN Priority=1 THEN 1 END) AS Priority1,
    COUNT(CASE WHEN Priority=2 THEN 1 END) AS Priority2,
    COUNT(CASE WHEN Priority=3 THEN 1 END) AS Priority3,
    COUNT(CASE WHEN Priority=4 THEN 1 END) AS Priority4,
    COUNT(CASE WHEN Priority=5 THEN 1 END) AS Priority5
FROM TableName
GROUP BY jobId, jobName

Answer 3

使用 ANSI SQL-92 CASE 语句，您可以执行以下操作（派生表加大小写）：

 SELECT jobId, jobName, SUM(Priority1)
 AS Priority1, SUM(Priority2) AS
 Priority2, SUM(Priority3) AS
 Priority3, SUM(Priority4) AS
 Priority4,  SUM(Priority5) AS
 Priority5 FROM (
     SELECT jobId, jobName,
     CASE WHEN Priority = 1 THEN 1 ELSE 0 END AS Priority1,
     CASE WHEN Priority = 2 THEN 1 ELSE 0 END AS Priority2,
     CASE WHEN Priority = 3 THEN 1 ELSE 0 END AS Priority3,
     CASE WHEN Priority = 4 THEN 1 ELSE 0 END AS Priority4,
     CASE WHEN Priority = 5 THEN 1 ELSE 0 END AS Priority5
     FROM TableName


)

Answer 4

IIF 不是标准的SQL构造，但是如果数据库支持，则可以实现更优雅的语句，产生相同的结果：

SELECT JobId, JobName,

COUNT(IIF (Priority=1, 1, NULL)) AS Priority1,
COUNT(IIF (Priority=2, 1, NULL)) AS Priority2,
COUNT(IIF (Priority=3, 1, NULL)) AS Priority3,
COUNT(IIF (Priority=4, 1, NULL)) AS Priority4,
COUNT(IIF (Priority=5, 1, NULL)) AS Priority5

FROM TableName
GROUP BY JobId, JobName