如何在MySQL中合并来自同一个表的查询

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'

我想把它们并排组合起来，就像这样：

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

---

我该怎么做呢？

您可以使用如下自连接

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'

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'

这应该可以做到（在Oracle中），而不需要自连接

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

---

OP想要列出所有

col_1

，并在

count

列中输入NULL，没有匹配的记录。是的，这就是我要找的。谢谢^_^

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