mySQL简单定义及四则运算

set @userName='王宇轩';
set @userName:='王与西安';
select @userName as'名称';
             
                         
                         
                         
                         
                         
                         
                         
                         
                         
                         
                         
                         
set @x=3,@y=5,@dx=3.156,@dy=6.778;
select @dx + @dy as'四则运算';
select @dx - @dy as'四则运算';
select @dx * @dy as'四则运算';
select @dx / @dy as'四则运算';




set @result1= @dx + @dy;
set @result2= @dx - @dy;
set @result3= @dx * @dy;
set @result4= @dx / @dy;
select @result1,@result2,@result3,@result4;
select round(@result1,2)

















set @x=7, @y=5;
select @x>@y as 'true',@x<=@y as 'false';

select @x=@y;

select TRUE AND TRUE;
select FALSE OR TRUE;

















set @userName='龙姑娘，王语嫣，赵灵儿';
set @set=17;
select * from student where userName=@userName or age =@age;
set @userName1='龙姑娘';
set @userName2='王语嫣';
set @userName3='赵灵儿';
select * from student where userName in (@userName1,@userName2,@userName3);

















select @@MAX_CONNECTIONS;
SELECT@@BINLOG_CACHE_SIZE;
select @@version as ''