如果我有一张这样的桌子:
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告图表,因此我需要显示 jobid、jobname 和 5 个名为 Priority1、Priority2、Priority3、Priority4 的字段。优先级5.
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
我如何以快速且高效的方式做到这一点?
我想你可能会追求
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),请删除它们并删除分组依据,
使用 COUNT 而不是 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
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
使用 ANSI SQL-92 CASE 语句,您可以执行以下操作(派生表加 case):
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
)
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
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
或者您可以在总和中使用 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
我需要显示 jobid、jobname 和 5 个名为 Priority1、Priority2、Priority3、Priority4 的字段。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的情况:每行都有四个带“0”的优先级列和一个带“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。
你真正想在这里展示什么?
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;