Question

SELECT COUNT(Type) from House where Type = 1
SELECT COUNT(Type) from House where Type = 2
SELECT COUNT(Type) from House where Type = 3

我的问题是：我想加入以上3个语句来获得：3列，例如： ColumnType1：'50'，ColumnType2：'60'，columnType3：'45'

感谢

Answer 1

您可以使用带有CASE表达式的聚合函数创建列：

SELECT 
  count(case when Type = 1 then Type end) as type_1,
  count(case when Type = 2 then Type end) as type_2,
  count(case when Type = 3 then Type end) as type_3
from House

Answer 2

如果case匹配

，您可以使用Type并加起来

SELECT sum(case when Type = 1 then 1 else 0 end) as type_1,
       sum(case when Type = 2 then 1 else 0 end) as type_2,
       sum(case when Type = 3 then 1 else 0 end) as type_3
from House

Answer 3

有一种更干净的SQL可以为您提供这个答案，但您将在不同的行上使用每种类型：

SELECT Type, COUNT(Type) FROM House GROUP BY Type

它的缺点是没有按照你的要求给你列;但优点是它适用于任何数量的不同类型，而无需更改查询。

Answer 4

SELECT
    COUNT(Type) as val1,
    (SELECT COUNT(Type) from House where Type = 2) as val2,
    (SELECT COUNT(Type) from House where Type = 3) as val3
from House where Type = 1

加入select语句以获取SQL中的列

4 个答案: