Question

您好我有一张表格如下 ID，学校，地址，城市，州，电话，电子邮件，传真。有近40个城市。我需要从每个城市中选择1个条目。任何人都可以指导我

例如

city 

 a1     30 entries

 a2     12 entries

......
 a40    36 entries

 Pick 1 from each a1,a40

Answer 1

一般情况下，我更喜欢通过JOIN到子查询来处理这些情况，如下例所示：

SELECT    s.id, s.school, s.address, s.city, s.phone, s.email, s.fax
FROM      schools s
JOIN      (SELECT   MAX(id) as max_id
           FROM     schools
           GROUP BY city) sub_s ON (sub_s.max_id = s.id);

JOIN实际上将结果集限制为具有不同城市的条目。这也假设您希望在每个城市有多个条目时选择具有最高ID的条目。如果您希望选择最低ID，则可以在子查询中使用MIN()聚合函数，而不是MAX()。

Answer 2

select * 
  from table_name 
 where id in (  select MAX(id) 
                  from table_name 
              group by city
             )

Answer 3

select * from your_table_name group by state, city

并使用随机选择

select * from your_table_name group by state, city order by rand()

Answer 4

在mysql中你可以简单地说：

select * from table group by city

Answer 5

SELECT DISTINCT city FROM tablename

mysql查询这个问题

5 个答案: