sql - 查询中的用户定义变量

Question

我一直在从事一个包含大量汇总统计数据的项目。对我很有帮助的一件事是设置一个变量，该变量集等于出现在每一行的查询结果。就像是

declare @totalpop int
set @totalpop = select count(*) as [population]
from myTable

select sex, count(sex), @totalpop
from myTable

忍者编辑我尝试过的查询，但失败了。错误是关键字选择附近的语法不正确

Answer 1

SELECT gender, count(gender) AS countGender, @totalPop AS totalPop 
FROM myTable  
GROUP BY gender

Answer 2

根据您的最后一段，这似乎是您想要的：

SELECT tsum.*, sum(cnt) over (partition by NULL) as TotalPop
FROM (SELECT gender, count(*) as cnt
      FROM t
      GROUP BY gender
     ) tsum

带有“over”子句的表达式是一个将所有窗口相加的窗口函数。

Answer 3

SELECT gender, count(gender), @totalPop
FROM myTable 

Answer 4

由于您使用@的是变量，我假设您使用的是 Sql Server。以下脚本返回一行，包含 3 列（每个计数一列）。我知道这不完全符合您的要求，但我想这是返回相同信息的一种简单方法：

DECLARE @COUNT_TOTAL INT;
DECLARE @COUNT_MALE INT;
DECLARE @COUNT_FEMALE INT;

SELECT @COUNT_TOTAL = COUNT(*)
  @COUNT_MALE = SUM(CASE WHEN gender='MALE' THEN 1 ELSE 0 END),
  @COUNT_FEMALE = SUM(CASE WHEN gender='FEMALE' THEN 1 ELSE 0 END),
FROM myTable;

SELECT @COUNT_TOTAL AS [COUNT_TOTAL]
    , @COUNT_MALE AS [COUNT_MALE]
    , @COUNT_FEMALE AS [COUNT_FEMALE];