Mysql 合计4个别名

我有以下疑问：

SELECT
    SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
    SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
    SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
    SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01'

哪些产出：

s1_count    s2_count    s3_count    s4_count    
  17           13           6           3

---

我想要另一个名为“total”的列，它包含所有4个别名的总和。

由于您不能在

SELECT

子句中使用列别名，因此有几种其他方法可以做到这一点。向查询中添加另一个条件聚合：

SELECT
SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count,
SUM(case when s1 = 'fel' or s2 = 'fel' or s3 = 'fel' or s4 = 'fel' then 1 else 0 end) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01'

注意，对于任何给定行，这假设只有

s1

、

s2

、

s3

或

s4

中的一个将等于

fel

更可靠的方法是将原始查询用作子查询：

SELECT *, s1_count+s2_count+s3_count+s4_count AS total
FROM (SELECT
      SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
      SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
      SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
      SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count
      FROM `arrest`
      WHERE date BETWEEN '2018-12-01' AND '2019-03-01') a

请注意，由于MySQL将数值上下文中的布尔表达式视为1（true）或0（false），因此可以按如下方式简化这些查询：

SELECT
SUM(s1 = 'fel') as s1_count,
SUM(s2 = 'fel') as s2_count,
SUM(s3 = 'fel') as s3_count,
SUM(s4 = 'fel') as s4_count,
SUM((s1 = 'fel') + (s2 = 'fel') + (s3 = 'fel') + (s4 = 'fel')) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01'

SELECT *, s1_count+s2_count+s3_count+s4_count AS total
FROM (SELECT
      SUM(s1 = 'fel') as s1_count,
      SUM(s2 = 'fel') as s2_count,
      SUM(s3 = 'fel') as s3_count,
      SUM(s4 = 'fel') as s4_count
      FROM `arrest`
      WHERE date BETWEEN '2018-12-01' AND '2019-03-01') a

---

这样做就消除了第一个查询要求任何给定行的

s1

、

s2

、

s3

或

s4

中只有一个等于

fel

的问题。

因为在

SELECT

子句中不能使用列别名，所以有几种其他方法可以做到这一点。向查询中添加另一个条件聚合：

SELECT
SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count,
SUM(case when s1 = 'fel' or s2 = 'fel' or s3 = 'fel' or s4 = 'fel' then 1 else 0 end) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01'

注意，对于任何给定行，这假设只有

s1

、

s2

、

s3

或

s4

中的一个将等于

fel

更可靠的方法是将原始查询用作子查询：

SELECT *, s1_count+s2_count+s3_count+s4_count AS total
FROM (SELECT
      SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
      SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
      SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
      SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count
      FROM `arrest`
      WHERE date BETWEEN '2018-12-01' AND '2019-03-01') a

请注意，由于MySQL将数值上下文中的布尔表达式视为1（true）或0（false），因此可以按如下方式简化这些查询：

SELECT
SUM(s1 = 'fel') as s1_count,
SUM(s2 = 'fel') as s2_count,
SUM(s3 = 'fel') as s3_count,
SUM(s4 = 'fel') as s4_count,
SUM((s1 = 'fel') + (s2 = 'fel') + (s3 = 'fel') + (s4 = 'fel')) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01'

SELECT *, s1_count+s2_count+s3_count+s4_count AS total
FROM (SELECT
      SUM(s1 = 'fel') as s1_count,
      SUM(s2 = 'fel') as s2_count,
      SUM(s3 = 'fel') as s3_count,
      SUM(s4 = 'fel') as s4_count
      FROM `arrest`
      WHERE date BETWEEN '2018-12-01' AND '2019-03-01') a

这样做可以消除第一个查询的问题，即对于任何给定行，只有

s1

、

s2

、

s3

或

s4

中的一个将等于

fel

。

您可以尝试：

SELECT s1_count, s2_count, s3_count, s4_count, 
       SUM(s1_count + s2_count + s3_count + s4_count) as total_count
FROM 
(
    SELECT
        SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
        SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
        SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
        SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count
    FROM `arrest`
    WHERE date BETWEEN '2018-12-01' AND '2019-03-01'
) q

您可以尝试：

SELECT s1_count, s2_count, s3_count, s4_count, 
       SUM(s1_count + s2_count + s3_count + s4_count) as total_count
FROM 
(
    SELECT
        SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
        SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
        SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
        SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count
    FROM `arrest`
    WHERE date BETWEEN '2018-12-01' AND '2019-03-01'
) q

---

不能重复使用别名。编写代码的最简单方法是在中使用

：

SELECT SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
       SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
       SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
       SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count,
       SUM(case when 'fel' in (s1, s2, s3, s4 ) then 1 else 0 end) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01';

实际上，整个查询可以简化为：

SELECT SUM( s1 = 'fel' ) as s1_count,
       SUM( s2 = 'fel' ) as s2_count,
       SUM( s3 = 'fel' ) as s3_count,
       SUM( s4 = 'fel' ) as s4_count,
       SUM( 'fel' in (s1, s2, s3, s4 ) ) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01';

MySQL将布尔值视为数字上下文中的数字，其中“1”表示true，“0”表示false。当您想要计算某个表达式的真值时，这非常方便。
您不能重复使用别名。编写代码的最简单方法是在

中使用

：

SELECT SUM(case when s1 = 'fel' then 1 else 0 end) as s1_count,
       SUM(case when s2 = 'fel' then 1 else 0 end) as s2_count,
       SUM(case when s3 = 'fel' then 1 else 0 end) as s3_count,
       SUM(case when s4 = 'fel' then 1 else 0 end) as s4_count,
       SUM(case when 'fel' in (s1, s2, s3, s4 ) then 1 else 0 end) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01';

实际上，整个查询可以简化为：

SELECT SUM( s1 = 'fel' ) as s1_count,
       SUM( s2 = 'fel' ) as s2_count,
       SUM( s3 = 'fel' ) as s3_count,
       SUM( s4 = 'fel' ) as s4_count,
       SUM( 'fel' in (s1, s2, s3, s4 ) ) as total
FROM `arrest`
WHERE date BETWEEN '2018-12-01' AND '2019-03-01';

MySQL将布尔值视为数字上下文中的数字，其中“1”表示true，“0”表示false。当您想计算某个表达式的真值时，这很方便。
在MySQL 5.7+、MySQL 8.0+中，此查询不起作用。在MySQL 5.7+、MySQL 8.0+中，此查询不起作用。