T-SQL两个使用不同的where子句计数

Question

我想计算具有不同where子句的表的值,并想知道是否有更好的方法.

在这段代码中,我算一个值.

SELECT v.name, count(v.value) AS v1
FROM dbo.table as v
WHERE v.organisationID = 2
AND v.datecreated > '2018-01-01'
AND v.datecreated < '2018-05-01'
AND v.value = 1
GROUP BY v.name

我还想计算所有值为value = 2的行,我的方式是这样的,使用子选择.

SELECT v.name, count(v.value) AS v1, (SELECT v2.name, count(v2.value)  
FROM dbo.table as v2
WHERE v2.organisationID = 2
AND v2.datecreated > '2018-01-01'
AND v2.datecreated < '2018-05-01'
AND v2.value = 2
GROUP BY v2.name) AS v2
FROM dbo.table as v
WHERE v.organisationID = 2
AND v.datecreated > '2018-01-01'
AND v.datecreated < '2018-05-01'
AND v.value = 1
GROUP BY v.name

该表包含> 1亿行,所以我真的想要最快的方式.我在表上使用聚簇列存储索引.

是否有一些方法可以通过子选择进行.

伪代码:

SELECT v.name, count(v.value where v.value=1) AS v1, count(v.value where v.value=2) AS v2
FROM dbo.table as v
WHERE v.organisationID = 2
AND v.datecreated > '2018-01-01'
AND v.datecreated < '2018-05-01'
GROUP BY v.name

Answer 1

是的，只需使用一个CASE表达式：

SELECT  v.name, 
        SUM(CASE WHEN v.value = 1 THEN 1 ELSE 0 END) AS v1,
        SUM(CASE WHEN v.value = 2 THEN 1 ELSE 0 END) AS v2
FROM dbo.table as v
WHERE v.organisationID = 2
AND v.datecreated > '2018-01-01'
AND v.datecreated < '2018-05-01'
AND v.value IN (1,2)
GROUP BY v.name
;