--查询基本使用
-- 查询所有列
--select * from 表名
select * from students;
--一定条件查询
select * from students where name='小李飞刀';
select * from students where id>3;
-- 查询制定列
select name, gender from students;
-- 可以使用as制定列或表制定别名;
select name as 姓名, gender as 性别 from students;
--字段的顺序
select id as 序号, gender as 性别, name as 姓名 from students;
--创建学生表
create table students (
id int unsigned not null auto_increment primary key,
name varchar(20) default '',
age tinyint unsigned default 0,
high decimal(5,2),
gender enum('男', '女', '中性', '保密') default '保密',
cls_id int unsigned default 0,
is_delete bit default 0
);
--创建班级表
create table classes(
id int unsigned auto_increment primary key not null,
name varchar(20) not null
);
--往students表里插入数据
insert into students values
(0,'小明',18,180.00,2,1,0),
(0,'小月月',19,180.00,2,2,0),
(0,'彭于晏',28,185.00,1,1,0),
(0,'刘德华',58,175.00,1,2,0),
(0,'黄蓉',108,160.00,2,1,0),
(0,'凤姐',44,150.00,4,2,1),
(0,'王祖贤',52,170.00,2,1,1),
(0,'周杰伦儿',34,null,1,1,0),
(0,'程坤',44,181.00,1,2,0),
(0,'和珅',55,166.00,2,2,0),
(0,'刘亦菲',29,162.00,3,3,0),
(0,'金星',45,180.00,2,4,0),
(0,'静香',18,170.00,1,4,0),
(0,'郭静',22,167.00,2,5,0),
(0,'周杰',33,178.00,1,1,0);
--向classes表里插入数据
insert into classes values (0, 'python_01期'),(0, 'python_02期');
--查询
-- 查询所有字段
select * from students;
select * from classes;
-- 查询制定的字段
select name, age from students;
-- 使用as给字段起别名
select name as 姓名, age as 年龄 from students;
-- 通过表名字查询
select students.name, students.age from students;
-- 给表起别名查询
select s.name, s.age from students as s;
--消除重复行
-- distinct
select distinct gender from students;
--条件查询
--比较运算符
-- 查询年纪大于18岁的信息
select * from students where age > 18;
select id, name, gender from students where age > 18;
--18岁到28岁之间(and)
select * from students where age>18 and age<28;
--在18岁以上或者身高180以上的人(or)
select * from students where age>18 or high>=180;
-- 模糊查询
-- like
-- % 替代1个或者多个甚至是没有
select * from students where name like '小%';
-- 查询姓名中有‘小’的所有名字
select * from students where name like '%小%';
-- 查询有两个字的名字
select * from students where name like '__';
-- 查询至少有2个字的名字
select * from students where name like '__%';
-- rlike 正则
-- 查询以周开始的名字
select * from students where name rlike '^周.*';
select * from students where name rlike '^周.*儿$';
--范围查询
-- in (1,3,8)表示在一个非连续的范围内
-- 查询 年纪为18,34的人
select * from students where age=18 or age=34;
select * from students where age=18 or age=34 or age=12;
select * from students where age in (12,18,34);
--查询 年龄在17岁到34岁之间的信息
select * from students where age between 18 and 34;--(不包含34岁)
--查询 年纪不在18到34岁的信息
select * from students where age not between 18 and 34;
-- 空判断
-- 判断is null
-- 查询身高为空的信息
select * from students where high is null;
-- 判断非空is not null
select * from students where high is not null;