CRUD:
create 增对应语句 insert
delete 删对应语句 delete
update 改对应语句 update
read 查对应语句 select

insert into 表名

insert into 表名 （字段1，字段2，...） values (字段1具体值，字段2具体值，...);
insert into 表名  values (字段1具体值，字段2具体值，...);  
插入全部字段时可省略 （字段1，字段2，...）

CREATE TABLE `emp`(
    id INT,
    `name` VARCHAR(32),
    `birthday` DATE,
    `gender` CHAR(1),
    `phone_number` CHAR(11),
    `entry_date` DATETIME,
    `job` VARCHAR(32),
    `salary` DOUBLE,
    `resume` TEXT
)
INSERT INTO `employee` VALUES(1,"张磊","1996-02-26","男","17864215200","2022-08-08 09-09-09","java开发工程师",25000,"这是我的简历");
INSERT INTO `employee` VALUES(2,"张杰","1996-07-26","男","17864215255","2018-08-08 09-09-09","python开发工程师",20000,"这是我的简历");

delete from 表名（慎用）

SELECT * FROM employee;
#1.删除表中特定行
DELETE FROM employee WHERE user_name='张杰';
#2.删除表中所有行
DELETE FROM employee

上面是emp表中的数据
下面演示把最后两行数据删除

使用select * from emp查看当前emp数据，由下图可知删除成功

总结：
delete from 表名 where子句
（where子句用于筛选行）

update 表名

SELECT * FROM employee;
#1.修改所有员工的salary为50000
#update table employee set salary=50000; 
UPDATE employee SET salary=50000;
#2.修改指定员工的salary为100000
UPDATE employee SET salary=100000 WHERE user_name='张磊';
#3.将指定员工的salary在原有基础上加50000
UPDATE employee SET salary=salary+50000 WHERE user_name='张磊';
#4.同时修改多个字段
UPDATE employee SET salary=salary+50000,job="java高级工程师" WHERE user_name='张磊';

update 表名 set 字段1=新值1，字段2=新增2,… where子句
where子句筛选行
set子句用于修改具体的字段

select 内容 from 表名

贯穿查询部分的三张表

#进入初级难度阶段
#部门表
CREATE TABLE dept(
    deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,
    dname VARCHAR(20) NOT NULL DEFAULT '',
    loc VARCHAR(13) NOT NULL DEFAULT ''
);
INSERT INTO dept VALUES (10,'accounting','NewYork');
INSERT INTO dept VALUES (20,'researching','Washington');
INSERT INTO dept VALUES (30,'sales','Houston');
INSERT INTO dept VALUES (40,'financing','LosAngeles');
INSERT INTO dept VALUES (50,'advertising','Miami');
SELECT * FROM dept;
DROP TABLE emp;
#员工表
CREATE TABLE emp(
    empno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 COMMENT '员工编号',
    ename VARCHAR(20) NOT NULL DEFAULT '' COMMENT '员工姓名',
    job VARCHAR(9) NOT NULL DEFAULT '' COMMENT '员工职位',
    mgr MEDIUMINT UNSIGNED COMMENT '上级编号',
    hiredate DATE NOT NULL COMMENT '入职日期',
    salary DECIMAL(7,2) NOT NULL COMMENT '运功薪水',
    bonus DECIMAL(7,2) COMMENT '员工红利',
    deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 COMMENT '部门编号'
)
INSERT INTO emp VALUES (7839,'KING','PRESIDENT',NULL,'1991-01-01',5000.00,NULL,10);
INSERT INTO emp VALUES (7566,'JONES','MANAGER',7839,'1991-01-02',2975.00,NULL,20);
INSERT INTO emp VALUES (7698,'BLAKE','MANAGER',7839,'1991-01-03',2985.00,NULL,30);
INSERT INTO emp VALUES (7782,'CLARK','MANAGER',7839,'1991-01-04',2995.00,NULL,10);
INSERT INTO emp VALUES (7902,'FORD','ANALYST',7566,'1993-01-04',1995.00,NULL,20);
INSERT INTO emp VALUES (7788,'SCOTT','ANALYST',7566,'1994-01-04',1985.00,NULL,20);
INSERT INTO emp VALUES (7782,'SMITH','CLERK',7902,'1995-01-04',995.00,NULL,20);
INSERT INTO emp VALUES (7934,'MILLER','CLERK',7782,'1996-01-04',985.00,NULL,10);
INSERT INTO emp VALUES (7499,'ALLEN','SALESMAN',7698,'1998-01-04',965.00,NULL,30);
INSERT INTO emp VALUES (7521,'WARD','SALESMAN',7698,'1999-01-04',955.00,NULL,30);
INSERT INTO emp VALUES (7654,'MARTIN','SALESMAN',7698,'1990-01-04',945.00,NULL,30);
INSERT INTO emp VALUES (7844,'TURNER','SALESMAN',7698,'1996-03-04',935.00,NULL,30);
SELECT * FROM EMP;
#工资级别表
CREATE TABLE salaryGrade(
    grade MEDIUMINT UNSIGNED NOT NULL DEFAULT 0,
    lowsal DECIMAL(7,2) NOT NULL,
    highsal DECIMAL(7,2) NOT NULL
);
INSERT INTO salaryGrade VALUES (1,900,1000);
INSERT INTO salaryGrade VALUES (2,1000,2000);
INSERT INTO salaryGrade VALUES (3,2000,3000);
INSERT INTO salaryGrade VALUES (1,3000,10000);
SELECT * FROM salaryGrade;

GroupBy好文

链接1

Java

语法2