DQL

#MySQL变量的定义与应用
set @userName='小可爱';
select @userName;
# 定义数值类型·整数·小数
set @x=5,@y=7;
select @x+@y, @x-@y, @x*@y,@x/@y;
#1、字符串查询
set @cityName='Haag';
SELECT * FROM city where `Name` =@cityName;
#2、数值类型
set @popvalue='105819';
select * from city where Population=@popvalue;