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 |
+------+------+
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 |
+------+------+