比如说 有个表
id title time
1 a 20120304
2 a 20121314
3 b 20121314
4 c 20121111
5 d 20121221
6 c 20121111
第一种想要的结果:
想查出title没有重复的数据 有没有办法
想要结果 为
id title time
3 b 20121314
5 d 20121221第二种想要的结果
第一种多加个条件,如果title相同 但是time也相同 那也显示出这条数据(仅一条)
id title time
3 b 20121314
4 c 20121111
5 d 20121221大家有没有好的办法
id title time
1 a 20120304
2 a 20121314
3 b 20121314
4 c 20121111
5 d 20121221
6 c 20121111
第一种想要的结果:
想查出title没有重复的数据 有没有办法
想要结果 为
id title time
3 b 20121314
5 d 20121221第二种想要的结果
第一种多加个条件,如果title相同 但是time也相同 那也显示出这条数据(仅一条)
id title time
3 b 20121314
4 c 20121111
5 d 20121221大家有没有好的办法
+------+-------+----------+
| id | title | time |
+------+-------+----------+
| 1 | a | 20120304 |
| 2 | a | 20121314 |
| 3 | b | 20121314 |
| 4 | c | 20121111 |
| 5 | d | 20121221 |
| 6 | c | 20121111 |
+------+-------+----------+
6 rows in set (0.00 sec)root@localhost : test 04:59:22>select a.* from tes a,(select title,count(*) from tes group by title having count(*)=1) b where a.title=b.title;
+------+-------+----------+
| id | title | time |
+------+-------+----------+
| 3 | b | 20121314 |
| 5 | d | 20121221 |
+------+-------+----------+
2 rows in set (0.00 sec)root@localhost : test 04:59:47>select id,title,time from tes group by title,time;
+------+-------+----------+
| id | title | time |
+------+-------+----------+
| 1 | a | 20120304 |
| 2 | a | 20121314 |
| 3 | b | 20121314 |
| 4 | c | 20121111 |
| 5 | d | 20121221 |
+------+-------+----------+
5 rows in set (0.00 sec)
+----+-------+----------+
| id | title | time |
+----+-------+----------+
| 1 | a | 20120304 |
| 2 | a | 20121314 |
| 3 | b | 20121314 |
| 4 | c | 20121111 |
| 5 | d | 20121221 |
| 6 | c | 20121111 |
+----+-------+----------+
6 rows in set (0.00 sec)mysql> select * from tb a where not exists(select id from tb b where b.title=a.title and b.id<>a.id);
+----+-------+----------+
| id | title | time |
+----+-------+----------+
| 3 | b | 20121314 |
| 5 | d | 20121221 |
+----+-------+----------+
2 rows in set (0.00 sec)mysql> select * from tb a where not exists(select id from tb b where b.title=a.title and b.id<>a.id and b.time<>a.time) group by a.title;
+----+-------+----------+
| id | title | time |
+----+-------+----------+
| 3 | b | 20121314 |
| 4 | c | 20121111 |
| 5 | d | 20121221 |
+----+-------+----------+
3 rows in set (0.00 sec)
貌似用not exists 加个select 的话 速度是不是很会很慢呀。。
select * from tt a where not exists(select 1 from tt where a.title=title and a.id<>id)
2select * from tt a where exists(select 1 from tt where a.title=title and a.time=time and a.id<id)
union
select * from tt a where not exists(select 1 from tt where ((a.title=title and a.id<>id)
or
(a.title=title and a.time=time and a.id<id)))
not exists效率确实挺高的
比not in好多了。好了 结贴了