如何在MySQL中结合来自同一个表的查询

时间:2009-08-24 08:22:24

标签: mysql union

我有两组结果:

SELECT name, count(appearance) as countA from table where results = '1'
SELECT name, count(appearance) as countB from table where results = '2'

我希望将它们并排组合,如下所示:

+---------+---------+---------+
| col_1   | countA  | countB  |
+---------+---------+---------+
| John    |    3    |    1    |
| Mary    |    1    |    2    |
| Gary    |    2    |   NULL  |
| Sean    |    4    |   NULL  |
| Mike    |  NULL   |    6    |
+---------+---------+---------+

我该怎么做?

4 个答案:

答案 0 :(得分:5)

这应该(在Oracle中)而不需要自联接

SELECT name
     , sum( case results when '1' then 1 else 0 end ) as countA 
     , sum( case results when '2' then 1 else 0 end ) as countB
  from table 
 where results IN ( '1', '2' )
 group by
       name

答案 1 :(得分:1)

您可以按如下方式使用自我加入

select a.col_1, a.countA, b.countB from table a, table b
where a.col_1 = b.col_1 and a.results='1' and b.results='2'

答案 2 :(得分:-1)

SELECT name, count(appearance) as countA, null AS countB from table where results = '1'
UNION ALL
SELECT name, null AS countA, count(appearance) as countB from table where results = '2'

答案 3 :(得分:-1)

SELECT `table`.name, countA, countB
FROM tab
LEFT OUTER JOIN
  (SELECT name, count(appearance) as countA from `table` where result = '1' group by name) as tmp1
ON `table`.name = tmp1.name
LEFT OUTER JOIN
  (SELECT name, count(appearance) as countB from `table` where result = '2' group by name) as tmp2
ON `table`.name = tmp2.name;