详解SQL中的DQL查询语言

select * from student; 查询英语在70到75之间的学生的信息-- select * from student where english BETWEEN 70 AND 75; 查询语文是80或者82或者90分的学生信息-- select * from student where chinese IN(80,82,90); 查询所有首字母为l的学生的成绩-- select * from student where name like "l%"; 查询数学大于80且语文大于80 的同学-- select * from student where math>80 and chinese>90; 对数学成绩排序后输出 （默认升序 ASC）-- select * from student order by math; 对数学成绩排序后输出（降序 DESC）-- SELECT * FROM student order by math DESC; 指定多个字段进行排序，先按第一个字段进行排序，如果相同则按第二个字段进行排序  -- SELECT * FROM student ORDER BY math DESC,chinese DESC; WHERE后可以加 ORDER BY-- SELECT * from student where name like "%l" ORDER BY math DESC; 显示student 表格中的前3行SELECT * from student LIMIT 2; 显示student 表格中的第3~5行SELECT * from student LIMIT 2,3; -- 2表示偏移量，3表示显示的行数

*②select |{column1|expression、column2|expression,…}from table;select column as 别名 from table;

create table customer( id int PRIMARY KEY auto_increment, name varchar (20) not null, adress varchar (20) not null);create table orders( order_num varchar(20) PRIMARY KEY, price FLOAT not NULL, customer_id int, -- 进行和customer 关联的字段 外键 constraint cus_ord_fk foreign key (customer_id) REFERENCES customer(id));insert into customer(name,adress) values("zs","北京");insert into customer(name,adress) values("ls","上海");SELECT * from customer;INSERT INTO orders values("010",30.5,1);INSERT INTO orders values("011",60.5,2);INSERT INTO orders values("012",120.5,1);SELECT * from orders;

primary key 主键 （auto_increment 设置自动增长）-- UNIQUE 表约束 唯一性标识-- PRIMARY KEY 主键 CREATE TABLE t4 ( id INT PRIMARY KEY auto_increment, NAME VARCHAR (20) NOT NULL, gender CHAR (5) NOT NULL, idCard VARCHAR (20) UNIQUE -- UNIQUE 唯一性标识);desc t4;insert into t4 (name,gender,idCard) VALUE("zs","man","110");insert into t4 (name,gender,idCard) VALUE("ls","woman","112");