Question

我有这样的数据库

id name group

使用这样的数据

1 john A
2 john B
3 charles B
4 peter B
5 rose B
6 charles A
7 justin C

正如您所看到的，可能性是一个ID与一个组或多个组相关联

我需要一个过滤的查询

a）在A组和B组 b）属于A组而不是B组 c）仅在A组

Answer 1

    a. select distinct name from tablename where group = 'A' or group = 'B';
    b. select distinct name from tablename where group = 'A' and group <> 'B';
    c. select distinct name from tablename where group = 'A' and 
         group not in (select distinct(t1.group) from tablename t1 
                         where t1.group <> 'A');

Answer 2

我喜欢使用group by和having子句来解决这些问题。第一个问题：

select name
from table
group by name
having sum(group = 'A') > 1 and sum(group = 'B') > 0;

另外两个是：

having sum(group = 'A') > 1 and sum(group = 'B') = 0;
having sum(group = 'A') > 1 and sum(group <> 'A') = 0;

SQL过滤组数据

2 个答案: