计算两个选择计数的百分比

Question

我有一个查询

select count(1) from table_a where state=1;

它给了20

select count(1) from table_a where state in (1,2);

它给了25

我想查询提取百分比80％（将是20 * 100/25）。可以只在一个查询中使用这些吗？

Answer 1

我认为没有测试，以下SQL命令可以做到这一点

SELECT SUM(CASE WHEN STATE = 1      THEN 1 ELSE 0 END)
      /SUM(CASE WHEN STATE IN (1,2) THEN 1 ELSE 0 END)
      as PERCENTAGE
FROM TABLE_A

或以下

SELECT S1 / (S1 + S2) as S1_PERCENTAGE
FROM
    (
    SELECT SUM(CASE WHEN STATE = 1 THEN 1 ELSE 0 END) as S1
          ,SUM(CASE WHEN STATE = 2 THEN 1 ELSE 0 END) as S2
    FROM TABLE_A
    )

或以下

SELECT S1 / T as S1_PERCENTAGE
FROM
    (
    SELECT SUM(CASE WHEN STATE = 1      THEN 1 ELSE 0 END) as S1
          ,SUM(CASE WHEN STATE IN (1,2) THEN 1 ELSE 0 END) as T
    FROM TABLE_A
    )

您可以选择性能或可读性！

Answer 2

正如@ schlebe的第一个查询略有不同，您可以通过制作条件继续使用count()：

select count(case when state = 1 then state end)
     / count(case when state in (1, 2) then state end) as result
from table_a

或乘以100得到百分比而不是小数：

select 100 * count(case when state = 1 then state end)
           / count(case when state in (1,2) then state end) as percentage
from table_a

Count忽略空值，如果不满足条件，则两个case表达式都默认为null（你可以使用else null使其显式化）。

使用CTE进行虚拟数据的快速演示：

with table_a(state) as (
            select 1 from dual connect by level <= 20
  union all select 2 from dual connect by level <= 5
  union all select 3 from dual connect by level <= 42
)
select 100 * count(case when state = 1 then state end)
           / count(case when state in (1,2) then state end) as percentage
from table_a;

PERCENTAGE
----------
        80

Answer 3

为什么plsql标签？无论如何，我认为你需要的是：

(select count(1) from table_a where state=1) * 100 /  (select count(1) from table_a where state in (1,2)) from dual