sql将多个查询合并为一个？

Question

请注意：NO JOIN请。

比方说，我得到了一个表user，字段名称gender。 gender值可以是0,1,-1。

我想知道那里的数量值分别。 我知道的是使用三个SQL查询如下。

select count(1) from user where gender=0 
select count(1) from user where gender=1 
select count(1) from user where gender=-1 

问题：如何将上述内容合并为一个查询？ btw，我是SQL的新手。

Answer 1

select gender, count(*) 
from user 
group by gender 

Answer 2

GROUP BY最有可能为您提供最好的服务。但是，您唯一的限制是“不加入”。这将允许（除GROUP BY）为

的

SELECT 
    (SELECT COUNT(1) FROM User WHERE gender = 0) AS genderNought 
    , (SELECT COUNT(1) FROM User WHERE gender = 1) AS genderOne 
    , (SELECT COUNT(1) FROM User WHERE gender = -1) AS genderMinusOne; 

和

SELECT COUNT(1) AS hits, gender, 'genderNought' AS genderInWords FROM User WHERE gender = 0 UNION ALL 
SELECT COUNT(1), gender, 'genderOne' FROM User WHERE gender = 1 UNION ALL 
SELECT COUNT(1), gender, 'genderMinusOne' FROM User WHERE gender = -1; 

一方为好。

参见SQL Fiddle。