mysql数据的增删改查
一、插入数据
INSERT INTO USER VALUES(1,'admin','1995-12-30',99.8);
给指定字段加数据
INSERT INTO USER(sname,birth) VALUES('tom','2020-06-17');
二、修改数据
UPDATE USER SET sname='jerry' WHERE sid=1;
UPDATE USER SET sid=2,chengji=100 WHERE sname='tom';
三、删除数据
DELETE FROM USER WHERE sid=2;
清空表
DELETE FROM USER ;
TRUNCATE USER;
TRUNCATE USER;删除的更加彻底无法找回
四、查询数据
全部查询*指全部字节
SELECT * FROM student;
查询某个字节的信息
SELECT sname,birth FROM USER;
查询时并给查询的字节起一个暂时的名字
SELECT sname AS '姓名',sex AS '性别',address FROM student;
查询时数字类型的数据可以进行运算
SELECT sname,(html+css+js) FROM student;
查询时去除重复的
SELECT DISTINCT sex FROM student;
SELECT DISTINCT(sex) FROM student;
指定条件查询
SELECT * FROM student WHERE sid=2;
SELECT * FROM student WHERE sex='男';
指定条件的或者（or）与并且（and）
SELECT sname FROM student WHERE sex='男' AND address='山东淄博';
SELECT sname FROM student WHERE sex='女' OR address='山东淄博';
可以运用比较运算符 <>不等于 between数字域（包含边界）
SELECT sid FROM student WHERE html>60;
SELECT * FROM student WHERE html<60 AND js>60;
SELECT sname FROM student WHERE address<>'山东淄博';
SELECT * FROM student WHERE html BETWEEN 60 AND 70;
SELECT * FROM student WHERE sname IS NOT NULL AND sname<>'';
模糊查询 关键词like
SELECT * FROM student WHERE sname LIKE '小%';
SELECT * FROM student WHERE sname LIKE '%红%';
SELECT * FROM student WHERE sname LIKE '__';
SELECT * FROM student WHERE sname LIKE '海__';
运算函数
SELECT SUM(html) FROM student; 求和
SELECT AVG(html) FROM student; 平均值
SELECT MIN(js) FROM student; 最小值
SELECT MAX(css) FROM student;最大值
SELECT COUNT(*) FROM student;列的总数
分页显示 关键词 limit
SELECT * FROM student LIMIT 0,2;
SELECT * FROM student LIMIT 2,2;/*
（当前页-1）*每页显示数，每页显示的条数*/
SELECT * FROM student ORDER BY html;
SELECT * FROM student WHERE html>60 ORDER BY html DESC;
SELECT * FROM student ORDER BY js DESC LIMIT 0,3;
SELECT * FROM student ORDER BY html,js DESC;
分组后查询
SELECT sex FROM student GROUP BY sex HAVING count(*)>2;
SELECT address FROM student GROUP BY address HAVING avg(html)>60;