select * from student;
– 查詢英語在70到75之間的學生的信息
-- select * from student where english BETWEEN 70 AND 75;

– 查詢語文是80或者82或者90分的學生信息
-- select * from student where chinese IN(80,82,90);

– 查詢所有首字母為l的學生的成績
-- select * from student where name like "l%";

– 查詢數(shù)學大于80且語文大于80 的同學
-- select * from student where math>80 and chinese>90;

– 對數(shù)學成績排序后輸出 （默認升序 ASC）
-- select * from student order by math;

– 對數(shù)學成績排序后輸出（降序 DESC）
-- SELECT * FROM student order by math DESC;

– 指定多個字段進行排序，先按第一個字段進行排序，如果相同則按第二個字段進行排序
  -- 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;

– 顯示student 表格中的前3行
SELECT * from student LIMIT 2;

– 顯示student 表格中的第3~5行
SELECT * from student LIMIT 2,3; -- 2表示偏移量，3表示顯示的行數(shù)

*②select |{column1|expression、column2|expression,…}from table;
select column as 別名 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, -- 進行和customer 關聯(lián)的字段 外鍵
 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 主鍵 （auto_increment 設置自動增長）
-- UNIQUE 表約束 唯一性標識
-- PRIMARY KEY 主鍵 
CREATE TABLE t4 (
 id INT PRIMARY KEY auto_increment,
 NAME VARCHAR (20) NOT NULL,
 gender CHAR (5) NOT NULL,
 idCard VARCHAR (20) UNIQUE -- UNIQUE 唯一性標識
);
desc t4;
insert into t4 (name,gender,idCard) VALUE("zs","man","110");
insert into t4 (name,gender,idCard) VALUE("ls","woman","112");