mysql - 如何在 MySQL 中合并来自同一张表的查询

Question

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'

我想将它们并排组合，如下所示：

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

我怎么做？

Answer 1

这应该在不需要自连接的情况下（在 Oracle 中）

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

Answer 2

您可以按如下方式使用自联接

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'

Answer 3

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'

Answer 4

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;