字段的条件计数

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。

因为我需要这个查询来生成报告图表，所以我需要显示 jobid、jobname 和 5 个字段，称为 Priority1、Priority2、Priority3、Priority4。优先级 5。

Priority1 应该计算优先级字段值为 1 的行数。

Priority2 应该计算优先级字段值为 2 的行数。

Priority3 应该计算优先级字段值为 3 的行数。

等

我将如何以快速高效的方式做到这一点？

Answer 1

SELECT  Priority, COALESCE(cnt, 0)
FROM    (
        SELECT  1 AS Priority
        UNION ALL
        SELECT  2 AS Priority
        UNION ALL
        SELECT  3 AS Priority
        UNION ALL
        SELECT  4 AS Priority
        UNION ALL
        SELECT  5 AS Priority
        ) p
LEFT JOIN
        (
        SELECT  Priority, COUNT(*) AS cnt
        FROM    jobs
        GROUP BY
                Priority
        ) j
ON      j.Priority = p.Priority

Answer 2

我需要显示 jobid、jobname 和 5 个字段，称为 Priority1、Priority2、Priority3、Priority4。优先级 5。

您的查询设计有问题。您也在每一行中显示一个特定的作业，因此您可能会遇到这样一种情况，即任何一行都有四个带有“0”的优先级列和一个带有“1”的优先级列（该作业的优先级）否则您最终会重复计算每一行的所有优先级。

你真的想在这里展示什么？

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

我想你可能会喜欢

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

但是我不确定您是否需要结果中的 jobID 和 JobName，如果需要删除它们并删除 group by，

Answer 5

您可以将表与自身连接起来：

select
   t.jobId, t.jobName,
   count(p1.jobId) as Priority1,
   count(p2.jobId) as Priority2,
   count(p3.jobId) as Priority3,
   count(p4.jobId) as Priority4,
   count(p5.jobId) as Priority5
from
   theTable t
   left join theTable p1 on p1.jobId = t.jobId and p1.jobName = t.jobName and p1.Priority = 1
   left join theTable p2 on p2.jobId = t.jobId and p2.jobName = t.jobName and p2.Priority = 2
   left join theTable p3 on p3.jobId = t.jobId and p3.jobName = t.jobName and p3.Priority = 3
   left join theTable p4 on p4.jobId = t.jobId and p4.jobName = t.jobName and p4.Priority = 4
   left join theTable p5 on p5.jobId = t.jobId and p5.jobName = t.jobName and p5.Priority = 5
group by
   t.jobId, t.jobName

或者你可以在 sum 中使用 case：

select
   jobId, jobName,
   sum(case Priority when 1 then 1 else 0 end) as Priority1,
   sum(case Priority when 2 then 1 else 0 end) as Priority2,
   sum(case Priority when 3 then 1 else 0 end) as Priority3,
   sum(case Priority when 4 then 1 else 0 end) as Priority4,
   sum(case Priority when 5 then 1 else 0 end) as Priority5
from
   theTable
group by
   jobId, jobName

Answer 6

使用 COUNT 代替 SUM 消除了对 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 7

IIF 不是标准 SQL 构造，但如果您的数据库支持它，您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

Answer 8

试试这个：

SELECT Count(Student_ID) as 'StudentCount' 
FROM CourseSemOne
where Student_ID=3 
Having Count(Student_ID) < 6 and Count(Student_ID) > 0;