查询

创建数据库、数据表

-- 创建数据库create database python_test_1 charset=utf8;-- 使用数据库use python_test_1;-- students表create table students( id int unsigned primary key auto_increment not null, name varchar(20) default '', age tinyint unsigned default 0, height 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);-- classes表create table classes ( id int unsigned auto_increment primary key not null, name varchar(30) not null);

准备数据

-- 向students表中插入数据insert into students values(0,'小明',18,180.00,2,1,0),(0,'小月月',18,180.00,2,2,1),(0,'彭于晏',29,185.00,1,1,0),(0,'刘德华',59,175.00,1,2,1),(0,'黄蓉',38,160.00,2,1,0),(0,'凤姐',28,150.00,4,2,1),(0,'王祖贤',18,172.00,2,1,1),(0,'周杰伦',36,NULL,1,1,0),(0,'程坤',27,181.00,1,2,0),(0,'刘亦菲',25,166.00,2,2,0),(0,'金星',33,162.00,3,3,1),(0,'静香',12,180.00,2,4,0),(0,'郭靖',12,170.00,1,4,0),(0,'周杰',34,176.00,2,5,0);-- 向classes表中插入数据insert into classes values (0, "python_01期"), (0, "python_02期");

查询所有字段

select * from 表名;例：select * from students;

查询指定字段

select 列1,列2,... from 表名;例:select name from students;

使用 as 给字段起别名

select id as 序号, name as 名字, gender as 性别 from students;

可以通过 as 给表起别名

-- 如果是单表查询 可以省略表明select id, name, gender from students;-- 表名.字段名select students.id,students.name,students.gender from students;-- 可以通过 as 给表起别名 select s.id,s.name,s.gender from students as s;

在select后面列前使用distinct可以消除重复的行

select distinct 列1,... from 表名;例：select distinct gender from students;