mysql - Mysql查询 - 分组结果

Question

我有 2 个表，基本上我喜欢做的是将结果或计数组合在一起以进行显示。尝试了不同版本的 mysql 语句，但没有得到任何结果。

2 个示例表是：

tbl_One  
index   O_priority
1         low
2         medium
3         high   

tbl_Two 
t_priority
2
1
3
3
2
3
1
1
1

expected results:
low =  4
medium =  2
high = 3 

Answer 1

SELECT T1.O_priority,T2.c FROM tbl_One as T1 LEFT JOIN (SELECT count(*) as c,t_priority FROM tbl_Two GROUP BY t_priority) as T2 ON T1.index = T2.t_priority;

Answer 2

加入表格，然后对结果进行分组：

SELECT   tbl_One.O_priority, COUNT(*)
FROM     tbl_One JOIN tbl_Two ON tbl_Two.t_priority = tbl_One.index
GROUP BY tbl_One.index

在sqlfiddle上查看。

Answer 3

尽可能简单，试试这个：

SELECT count(o.index) as `index`, o.O_priority 
FROM tbl_One o join tbl_two t on t.t_priority = o.index
group by t.t_priority;

SQL小提琴