mysql中有没有求两列差的函数?直接相减么?还有若是将求差后的数进行排序 是不是就不会用到索引了??
mysql> select * from test;
+------+-----+------+
| id | idd | name |
+------+-----+------+
| 1 | 200 | |
| 2 | 30 | |
| 3 | 40 | |
| 4 | 50 | |
| 18| 2 | |
| 20 | 8 | |
+------+-----+------+
6 rows in set (0.01 sec)
要求是:求idd-id的值并按idd-id倒序排序,取最大值。
mysql> select * from test;
+------+-----+------+
| id | idd | name |
+------+-----+------+
| 1 | 200 | |
| 2 | 30 | |
| 3 | 40 | |
| 4 | 50 | |
| 18| 2 | |
| 20 | 8 | |
+------+-----+------+
6 rows in set (0.01 sec)
要求是:求idd-id的值并按idd-id倒序排序,取最大值。
解决方案 »
- xtrabackup添加--slave-info参数全备失败, InnoDB: Operating system error number 2
- 【求助】求所有用户记录。
- 有没有什么办法可以把mysql回滚到某一时间?注意,是回滚,有些挺重要的数据给丢失了……所有文件齐全
- 有关MySql中 位函数 & 的问题
- 郁闷中,关于MySql 中 MySqlParameter的问题,在线等
- 请问在mysql下面如何删除两个以上的分类?
- mssql->mysql 后为何出现'\r\n'字符
- MYSQL语法错误
- 联表查询求救
- 求帮忙!这个sql语句该咋写
- mysql两列想减负数显示问题
- 请教一个读取日期的问题
order by idd-id desc limit 1
or
select max(idd-id) from tt
+------+------+------+
| id | idd | name |
+------+------+------+
| 1 | 200 | |
| 2 | 30 | |
| 3 | 40 | |
| 4 | 50 | |
| 18 | 2 | |
| 20 | 8 | |
+------+------+------+
6 rows in set (0.00 sec)mysql> select * from tb order by idd-id desc limit 1;
+------+------+------+
| id | idd | name |
+------+------+------+
| 1 | 200 | |
+------+------+------+
1 row in set (0.00 sec)
+------+------+------+
| id | idd | name |
+------+------+------+
| 1 | 200 | NULL |
| 2 | 30 | NULL |
| 3 | 40 | NULL |
| 4 | 50 | NULL |
| 18 | 2 | NULL |
| 20 | 8 | NULL |
+------+------+------+
6 rows in set (0.00 sec)mysql> select idd-id,id,idd,name from test order by 1 desc ;
+--------+------+------+------+
| idd-id | id | idd | name |
+--------+------+------+------+
| 199 | 1 | 200 | NULL |
| 46 | 4 | 50 | NULL |
| 37 | 3 | 40 | NULL |
| 28 | 2 | 30 | NULL |
| -12 | 20 | 8 | NULL |
| -16 | 18 | 2 | NULL |
+--------+------+------+------+
6 rows in set (0.00 sec)mysql> select idd-id,id,idd,name from test order by 1 desc limit 1;
+--------+------+------+------+
| idd-id | id | idd | name |
+--------+------+------+------+
| 199 | 1 | 200 | NULL |
+--------+------+------+------+
1 row in set (0.01 sec)mysql>
+----------------------+------+-----+------+
| idd-id | id | idd | name |
+----------------------+------+-----+------+
| 18446744073709551614 | 10 | 8 | |
| 199 | 1 | 200 | |
| 46 | 4 | 50 | |
| 37 | 3 | 40 | |
| 28 | 2 | 30 | |
| 1 | 1 | 2 | |
+----------------------+------+-----+------+
为什么不是负数???