MySQL title

1. increase

1.1 Add data for the specified field in the table

INSERT INTO Table name （ Field name 1, Field name 2,…）VALUES（ value 1, value 2,…）

INSERT INTO `user`(id,role) VALUES(3,"admin");

1.2 Add data for all fields in the table （ Can not specify a field ）

INSERT INTO Table name VALUES( value 11, value 2,…）;

INSERT INTO `user` VALUES(5,"lsy","lsy1234","admin");

1.3 Add multiple pieces of data at the same time

INSERT INTO `user` VALUES(6,"lsy","lsy1234","admin"),
                         (7,"lsy7","lsy1234","admin"),
                         (8,"lsy8","lsy1234","admin");

2. Delete

2.1 Delete some data

DELETE from user where username="lsy"

2.2 Delete all data

DELETE from user 

3. Change

3.1 Modify some data

UPDATE user set role="admin1" where id=9

3.2 Modify all data

UPDATE user set role="admin2" 

4. check

4.1 Simple query

select id,role from user
select * from user
select id,role from user where id<10
select id,role from user where id in (9,10)
select id,role from user where id BETWEEN 2 and 10
select id,role from user where role is NULL
select id,role from user where role like "adm%"（% Match any length of string , Include empty string .）
select id,role from user where role like "adm_"（ The underscore wildcard matches only a single character ）
select id,role from user where role like "admi_" and username="shiro"（AND  Has a higher priority than  OR）
select id,role from user where role like "admi_" or username="shiro"

4.2 Advanced query

SELECT COUNT(*) FROM user
SELECT sum(id) FROM user
SELECT avg(id) FROM user
SELECT max(id) FROM user
SELECT min(id) FROM user
SELECT *from user order by id DESC
SELECT COUNT(*) ,gender FROM user GROUP BY gender;
SELECT sum(grade),gender FROM user GROUP BY gender HAVING SUM(grade) < 300;
SELECT * from user   LIMIT 2 

4.3 Subquery

SELECT * FROM user where id=(SELECT MAX(id) from user)
SELECT * FROM (SELECT MAX(id) from user) as user1

4.4 Table joins

SELECT * FROM user u INNER JOIN role r on u.id=r.id 
SELECT * FROM user u LEFT JOIN role r on u.id=r.id 
SELECT * FROM user u RIGHT JOIN role r on u.id=r.id 
SELECT * FROM user u LEFT JOIN role r on u.id=r.id UNION SELECT * FROM user u RIGHT JOIN role r on u.id=r.id