变量在SQL当中的使用

set @userName='小可爱';
set @userName='小哈尼';
select @userName='海绵宝宝';
select @userName as '名称';
set @userName1='玛卡巴卡',@userName2='汤不理多',@userName3='胡西迪西';
select @userName1,@userName2,@userName3;


set @x=5.@y=0,@dx=0.1,@dy=5.56;
select @x + @y;
select @x - @y;
select @x * @y;
select @x / @y;
select @x % @y;
set @result1=@dx + @dy;
set @result2=@dx - @dy;
set @result3=@dx * @dy;
set @result4=@dx / @dy;
set @result5=@dx % @dy;
select @result1,@result2,@result3,@result4,@result5;

select ROUND(select @dx / @dy,2);#无法使用


set @x=5,@y=7;
select @x<= @y;
select @x> @y;
select @x= @y;


select TRUE and TRUE;
select FALSE OR TRUE;

set @userName='龙姑娘';
set @age=16;
select * from student where userName=@userName or age=@age;
set @userName1='龙姑娘';
set @userName2='赵灵儿';
select * from student where userName in(@userName1,@userName2);