1、单表和多表查询
1.1 算术运算符、比较运算符及特殊运算符
1)MySQL的算术运算符
select 0.1+0.3333,0.1-0.3333,0.1*0.3333,1/2,1%2;
select 1/0,100%0;
select 3%2,mod(3,2);
2)MySQL的比较运算符
select 1=0,1=1,null=null;
select 1<>0,1<>1,null<>null;
select 1<=>1,2<=>0,0<=>0,null<=>null;
select ‘a’<‘b’,’a’<‘a’,’a’<‘c’,1<2;
select ‘bdf’>’b’,’b’,<=‘b’,0<1;
select ‘a’>’b’,’abc’&g