mysql - 同一个表上具有不同 where 子句的两个选择查询

Question

我有一个表关注者和关注者计数..

想在一个存储过程中获得两者的计数..是否可以在同一个表上有两个具有不同 where 条件的选择查询？

CREATE TABLE Table1
    ([val1] int, [val2] int, [val3] int, [val4] int, other int)
;

INSERT INTO Table1
    ([val1], [val2], [val3], [val4], other)
VALUES
    (1, 26, 13, 1, 1),
    (2, 13, 26, 1, 1),
(3, 10, 26, 1, 1),
(4, 26, 13, 1, 1),
(5, 14, 26, 1, 1)
;

我的选择查询

(select count(*) as following_count from table1 where val2=26)

(select count(*) as follower_count from table1 where val3=26)

SQL FIDDLE LINK

Answer 1

为什么不使用 UNION ALL 触发这两个语句？

参见:http://dev.mysql.com/doc/refman/5.1/de/union.html

所以:

SELECT COUNT(*) AS following_count FROM table1 WHERE val2=26
UNION ALL
SELECT COUNT(*) AS following_count FROM table1 WHERE val3=26

在 1 个查询中返回包含 2 个数字的两行。

在两列中执行此操作:

SELECT
  (SELECT COUNT(*) AS following_count FROM table1 WHERE val2=26) col1
  , (SELECT COUNT(*) AS following_count FROM table1 WHERE val3=26) col2