MYSQL操作

设定变量
set @a:=1;         //普通变量赋值使用:=
set global @@sort_buffer_size=100;  //全局变量赋值
set @@global.sort_buffer_size=100;
set session @@sort_buffer_size=400; //session变量赋值
set @@session.sort_buffer_size=400;
set sort_buffer_size=400;           //默认session赋值
查询变量
select @a;                //查看普通变量
select @@global.sort_buffer_size;      //查看全局变量
show global variables like 'sort_buffer_size';
select @@session.sort_buffer_size;     //查看session变
量
show session variables like 'sort_buffer_size';
select @@sort_buffer_size;        //默认查看session变量
使用变量
select @t1:=(@t2:=1)+(@t3:=4),@t1,@t2,@t3;
+------------------------+------+------+------+
| @t1:=(@t2:=1)+(@t3:=4) | @t1  | @t2  | @t3  |
+------------------------+------+------+------+
|                      5 | 5    | 1    | 4    |
+------------------------+------+------+------+
select * from tt;
+------+------+
| id   | name |
+------+------+
|    1 | aa   |
|    2 | bb   |
+------+------+
select (@aa:=id) as a,(@aa+1) as b from tt;
+------+------+
| a    | b    |
+------+------+
|    1 |    2 |
|    2 |    3 |
+------+------+