不是专业后端的，所有可能有些不太准确，都是自己平时在项目当中总结的，谢谢ฅฅ*
添加/insert
给指定字段添加数据
INSERT INTO 表名 字段名 VALUES 值
INSERT INTO ninth_student (id,name,sex,age,weight,birth) VALUES (0,'亚亚','女',18,47,'2002-05-23')给全部字段添加数据
INSERT INTO 表名 VALUES 值
批量添加数据
INSERT INTO 表名 字段名 VALUES 值1,值2
INSERT INTO 表名 VALUES 值1,值2
INSERT INTO ninth_student VALUES (0,'哎亚亚','男',20,50,'2003-04-16'),(0,'SUN亚蛋','女',21,47,'2002-09-08'),(0,'哈哈哈','男',25,80,'1998-02-01'),(0,'嘎嘎嘎','男',30,75,'1993-05-12'),(0,'噜啦啦','女',23,52,'2000-11-28')修改/update
UPDATE 表名 set 字段名=值 WHERE 条件
UPDATE ninth_student set birth='2005-04-07' WHERE id=1一定要加where条件，要不然会修改整张表的所有数据
删除/delete
DELETE FROM 表名 WHERE 条件
DELETE FROM ninth_student WHERE id=8一定要加where条件，要不然会删除整张表的所有数据
查询/select
基本查询
SELECT 字段名 from 表名
SELECT id,name,sex,age,weight,birth from ninth_student条件查询
用where表示查询的条件
SELECT 字段名 from 表名 WHERE 条件
SELECT id,name,age,sex,weight,birth from ninth_student WHERE id BETWEEN 1 and 5SELECT 字段名 from 表名 WHERE 条件 and/or 条件
SELECT id,name,age,sex,weight,birth from ninth_student WHERE id>5 and sex='男'SELECT id,name,age,sex,weight,birth from ninth_student WHERE id>5 OR sex='男'模糊查询/like
利用%
SELECT id,name,age,sex,weight,birth from ninth_student WHERE name LIKE '%亚'SELECT id,name,age,sex,weight,birth from ninth_student WHERE name LIKE '亚%'SELECT id,name,age,sex,weight,birth from ninth_student WHERE name LIKE '%亚%'利用_,一个_代表一个字符，如果前面有两个字，就加两个
SELECT id,name,age,sex,weight,birth from ninth_student WHERE name LIKE '_马'分页查询/limit
SELECT 字段名 表名 LIMIT (n-1)*每页展示个数,每页展示个数
SELECT id,name,age,sex,weight,birth from ninth_student LIMIT 0,4SELECT id,name,age,sex,weight,birth from ninth_student LIMIT 4,4排序
SELECT 字段名 from 表名 ORDER BY age ASC/DESC
SELECT id,name,age,sex,weight,birth from ninth_student ORDER BY age ASCSELECT id,name,age,sex,weight,birth from ninth_student ORDER BY id DESC聚合函数
SELECT COUNT(0) from 表名：表示总共有几条数据
SELECT SUM(字段名) from 表名：求和
SELECT AVG(字段名) from 表名：平均数
SELECT MIN(字段名) from 表名：最大
SELECT MAX(字段名) from 表名：最小
SELECT CAST(AVG(字段名) as DECIMAL(10,0)) as AVG from 表名：类型转换
SELECT COUNT(0) from ninth_studentSELECT SUM(age) from ninth_studentSELECT AVG(age) from ninth_studentSELECT MIN(age) from ninth_studentSELECT MAX(age) from ninth_studentSELECT CAST(AVG(age) as DECIMAL(10,0)) as AVG from ninth_student分组查询
SELECT 字段名,聚合函数 from 表名 GROUP BY 字段名
GROUP BY 字段名：根据…分组
group by 分组字段，select后跟的也是相应的分组字段，他俩是一致的
where是分组前，having是分组后
having后面跟条件的话，也只能跟聚合函数
SELECT sex,COUNT(0),AVG(age) from ninth_student GROUP BY sexSELECT sex,COUNT(0),AVG(age) from ninth_student WHERE age>22 GROUP BY sex HAVING AVG(age)>20子查询
把查询到的结果当做另一个查询的条件
SELECT 字段名 from 表1 WHERE 字段名1 = (SELECT 表1_字段名1 from 表 WHERE 字段名='值')
SELECT name from dept WHERE id = (SELECT dept_id from ninth_student WHERE name='小马')内连接
多表联查，一定要待条件！！！
inner join 表示内连接
on 表和表之间的连接，只能用on
inner join … on … 只要看见join就加on
看到,就写where
SELECT 表1.字段名1,表1.字段名1,字段名1,字段名1,字段名1,字段名1,表2.字段名2,表2.字段名2 from 表1 INNER JOIN 表2 ON 表1.字段名1 = 表2.字段名2
SELECT ninth_student.id,ninth_student.name,age,sex,weight,birth,dept.id,dept.name from ninth_student INNER JOIN dept ON ninth_student.id = dept.idSELECT ninth_student.id,ninth_student.name,age,sex,weight,birth,dept.id,dept.name from ninth_student,dept WHERE ninth_student.dept_id = dept.idSELECT ninth_student.id,ninth_student.name,age,sex,weight,birth,dept.id,dept.name from ninth_student,dept WHERE ninth_student.id = dept.id外连接
在实际开发中，左外连接用的比较多
left join查询左边表的所有部分和右边表的交集，就是以左边的表为主
左外是以左边的表为主表，查询的结果只关注左表，不在乎右边
right join查询的是右边表的所有部分和左边表的交集，就是以右边的表为主
SELECT ninth_student.id,ninth_student.name,sex,age,weight,birth,dept.id,dept.name from dept LEFT JOIN ninth_student ON ninth_student.dept_id = dept.idSELECT ninth_student.id,ninth_student.name,sex,age,weight,birth,dept.id,dept.name from dept RIGHT JOIN ninth_student ON ninth_student.dept_id = dept.id