mysql之select 查询表数据（一）

1，select * 用于选择表中的所有列

select * from students;

2,单独查询某些列，用逗号隔开即可

select name,score from students;

3,配合where让查询更精确的关键词有以下：

-----and,or ,>,< >=,<= ,=,<>不等于,in,not in,between and,not匹配相反,not null非空
----like 搭配通配符_：一个字符，%：一个或多个字符
----example:
      select * from students where gender = '女' and name = '小梅';
      select * from students where birthday > '1993-04-05';
      select * from students where id in (1,3);
      select * from students where id = 1 or name = '小红'; 
      select * from students where name like '小%';
      select * from students where id <> 2;
      select * from students where name like '_东%';

4，在表dual 可用于计算

----加(+)、减(-)、乘(*)、除(/)、求于(也叫模运算%)等等
select  2*3 from dual;

注：如果插入数据有单引号，必须用单引号’或反斜杠\转义