mysql的学习-数据库表的记录的操作

Posted 2020-11-19 SZUhg

 

INSERT INTO bookcategory(category_id,category,parent_id) VALUES(1,‘计算机‘,0);//指定插入的顺序


INSERT INTO bookcategory VALUES(1,‘计算机‘,0);//按照默认的插入


INSERT INTO bookcategory(category_id,category,parent_id) VALUES(1,‘计算机‘,0)，(2,‘xxx‘,3)(3,‘xxxxx‘,4);//同时插入多条数据


INSERT INTO bookcategory SELECT * FROM test WHERE id>5//将查询结果插入表中


CREATE TABLE TEXT(

    category_id INT PRIMARY KEY AUTO_INCREMENT,

    parent_id INT NOT NULL

)AUTO_INCREMENT=5;    //auto_increment让这一列自动设置编号，默认初始值为,最后为设置初始值为5



ALTER TABLE bookcategory MODIFY category_id INT AUTO_INCREMENT=X//为已有表添加自增列



ALTER TABLE bookcategory MODIFY category_id INT;//去掉自增列


//有外键关系的话添加自增，要先去掉外键关系。


ALTER TABLE bookinfo DROP FOREIGN KEY fk_bcid//去掉外键


ALTER TABLE bookinfo ADD CONSTRAINT fk_bcid FOREIGN KEY(bookcdategory_id) REFERENCES bookcategory(category_id);//添加外键


SELECT price FROM bookinfo WHERE book_id=201501;//查询book_id为201501书的价格


SELECT * FROM readerinfo//查看读者信息表


SELECT xxx,xxx,xxx FROM readerinfo//查询指定列


SELECT xxx,xxx,xxx FROM readerinfo WHERE press=‘机械工业‘//设置外加条件的查询


SELECT DISTINCT press FROM bookinfo;//显示不重复的查询


SELECT * FROM readerinfo WHERE age IS NULL;//查询为空的列


UPDATE readerinfo SET balance =balance -18.9*0.05 WHERE card_id=‘xxxxxxxx‘//更新readerinfo这个表中的card_id为xxx的balance


DELETE FROM readerinfo WHERE card_id=‘201531513133‘//单表数据记录的删除,不加where则为全部删除


TRUNCATE TABLE readerinfo;//删除原表再创建空表


SELECT COUNT(*) FROM readerinfo WHERE sex=‘男‘//对查询结果的分组


SELECT sex FROM readerinfo GROUP BY sex;//查询有多少种性别


SELECT sex COUNT(*) FROM readerinfo GROUP BY sex;//统计每种性别的人数


SELECT sex FROM readerinfo GROUP BY sex WHERE COUNT(sex)>3;//也可以加限制条件。统计每种性别的人数


SELECT     * FROM bookinfo ORDER BY price//对查询结果排序，默认为升序


SELECT     * FROM bookinfo ORDER BY price,store;//price相同的，按照库存排序


SELECT * FROM bookinfo ORDER BY price ASC,store DESC;//asc升序，desc降序


SELECT * FROM bookinfo LIMIT 3;//limit限制查询数量，偏移量为0开始,显示前三行


SELECT * FROM bookinfo LIMIT 2,2;//显示第二条语句的后两个语句


SELECT store,COUNT(*) FROM bookinfo GROUP BY store ORDER BY store DESC LIMIT 4;//统计库存个数，并降序排序，并查看前四条语句

 

 

INSERT INTO bookcategory(category_id,category,parent_id) VALUES(1,‘计算机‘,0);//指定插入的顺序
INSERT INTO bookcategory VALUES(1,‘计算机‘,0);//按照默认的插入
INSERT INTO bookcategory(category_id,category,parent_id) VALUES(1,‘计算机‘,0)，(2,‘xxx‘,3)(3,‘xxxxx‘,4);//同时插入多条数据
INSERT INTO bookcategory SELECT * FROM test WHERE id>5//将查询结果插入表中
CREATE TABLE TEXT(
category_id INT PRIMARY KEY AUTO_INCREMENT,
parent_id INT NOT NULL
)AUTO_INCREMENT=5; //auto_increment让这一列自动设置编号，默认初始值为,最后为设置初始值为5
ALTER TABLE bookcategory MODIFY category_id INT AUTO_INCREMENT=X//为已有表添加自增列
ALTER TABLE bookcategory MODIFY category_id INT;//去掉自增列
//有外键关系的话添加自增，要先去掉外键关系。
ALTER TABLE bookinfo DROP FOREIGN KEY fk_bcid//去掉外键
ALTER TABLE bookinfo ADD CONSTRAINT fk_bcid FOREIGN KEY(bookcdategory_id) REFERENCES bookcategory(category_id);//添加外键
SELECT price FROM bookinfo WHERE book_id=201501;//查询book_id为201501书的价格
SELECT * FROM readerinfo//查看读者信息表
SELECT xxx,xxx,xxx FROM readerinfo//查询指定列
SELECT xxx,xxx,xxx FROM readerinfo WHERE press=‘机械工业‘//设置外加条件的查询
SELECT DISTINCT press FROM bookinfo;//显示不重复的查询
SELECT * FROM readerinfo WHERE age IS NULL;//查询为空的列
UPDATE readerinfo SET balance =balance -18.9*0.05 WHERE card_id=‘xxxxxxxx‘//更新readerinfo这个表中的card_id为xxx的balance
DELETE FROM readerinfo WHERE card_id=‘201531513133‘//单表数据记录的删除,不加where则为全部删除
TRUNCATE TABLE readerinfo;//删除原表再创建空表
SELECT COUNT(*) FROM readerinfo WHERE sex=‘男‘//对查询结果的分组
SELECT sex FROM readerinfo GROUP BY sex;//查询有多少种性别
SELECT sex COUNT(*) FROM readerinfo GROUP BY sex;//统计每种性别的人数
SELECT sex FROM readerinfo GROUP BY sex WHERE COUNT(sex)>3;//也可以加限制条件。统计每种性别的人数
SELECT * FROM bookinfo ORDER BY price//对查询结果排序，默认为升序
SELECT * FROM bookinfo ORDER BY price,store;//price相同的，按照库存排序
SELECT * FROM bookinfo ORDER BY price ASC,store DESC;//asc升序，desc降序
SELECT * FROM bookinfo LIMIT 3;//limit限制查询数量，偏移量为0开始,显示前三行
SELECT * FROM bookinfo LIMIT 2,2;//显示第二条语句的后两个语句
SELECT store,COUNT(*) FROM bookinfo GROUP BY store ORDER BY store DESC LIMIT 4;//统计库存个数，并降序排序，并查看前四条语句