MySQL的@与@@区别

MySQL的@与@@区别

@x 是 用户自定义的变量  (User variables are written as @var_name)

@@x 是 global或session变量  (@@global  @@session )

@@查看全局变量:

select   @@log_error;

@设置全局变量值:

mysql> SET @t1=0, @t2=0, @t3=0;

mysql> SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;