计算按组返回的记录数

Question

如何通过查询计算组返回的记录数,

例如:

select count(*) 
from temptable
group by column_1, column_2, column_3, column_4

给我,

1
1
2

我需要计算上述记录,得到1 + 1 + 1 = 3.

Answer 1

您可以使用另一个COUNT上的OVER子句在一个查询中执行这两个操作

select
    count(*) RecordsPerGroup,
    COUNT(*) OVER () AS TotalRecords
from temptable
group by column_1, column_2, column_3, column_4

Answer 2

最简单的解决方案是使用派生表:

Select Count(*)
From    (
        Select ...
        From TempTable
        Group By column_1, column_2, column_3, column_4
        ) As Z

另一种解决方案是使用Count Distinct:

Select ...
    , ( Select Count( Distinct column_1, column_2, column_3, column_4 )
        From TempTable ) As CountOfItems
From TempTable
Group By column_1, column_2, column_3, column_4

Answer 3

我知道现在已经很晚了,但没有人建议:

select count ( distinct column_1, column_2, column_3, column_4) 
from   temptable

这至少在Oracle中有效 - 我目前没有其他数据库可以测试它,我对T-Sql和MySQL语法不太熟悉.

另外,我不完全确定在解析器中以这种方式执行它是否更有效,或者是否其他人的嵌套select语句的解决方案更好.但是从编码的角度来看,我觉得这个更优雅.

Answer 4

我试图在没有子查询的情况下实现相同的目标,并且能够获得如下所需的结果

SELECT DISTINCT COUNT(*) OVER () AS TotalRecords
FROM temptable
GROUP BY column_1, column_2, column_3, column_4

Answer 5

怎么样：

SELECT count(column_1)
FROM
    (SELECT * FROM temptable
    GROUP BY column_1, column_2, column_3, column_4) AS Records

Answer 6

CTE 为我工作：

with cte as (
  select 1 col1
  from temptable
  group by column_1
)

select COUNT(col1)
from cte;