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数据库Mysql的学习(四)-表的记录操作

来源:http://www.mrmtshipyard.com 作者:时时彩平台 时间:2019-11-16 10:04

#mysql中 对于查询结果只显示n条三番两次行的难点#

在领扣上遇见的一个主题材料:求满足条件的连天3行结果的显示

X city built a new stadium, each day many people visit it and the stats are saved as these columns: id, date, people;
Please write a query to display the records which have 3 or more consecutive rows and the amount of people more than 100(inclusive).
For example, the table stadium:
+------+------------+-----------+
| id   | date       | people    |
+------+------------+-----------+
| 1    | 2017-01-01 | 10        |
| 2    | 2017-01-02 | 109       |
| 3    | 2017-01-03 | 150       |
| 4    | 2017-01-04 | 99        |
| 5    | 2017-01-05 | 145       |
| 6    | 2017-01-06 | 1455      |
| 7    | 2017-01-07 | 199       |
| 8    | 2017-01-08 | 188       |
+------+------------+-----------+

For the sample data above, the output is:
+------+------------+-----------+
| id   | date       | people    |
+------+------------+-----------+
| 5    | 2017-01-05 | 145       |
| 6    | 2017-01-06 | 1455      |
| 7    | 2017-01-07 | 199       |
| 8    | 2017-01-08 | 188       |
+------+------------+-----------+

1.第后生可畏先举行结果集的询问

select id,date,people from stadium where people>=100;

2.给查询的结果集扩充八个自增列

SELECT @newid:=@newid+1 AS newid,test.* 
FROM(SELECT @newid:=0)r, test WHERE people>100

3.自增列和id的差值 相像即延续

SELECT @newid:=@newid+1 AS newid,test.* ,@cha:=id-@newid AS cha 
FROM(SELECT @newid:=0)r, test WHERE people>100

4.将长期以来的差值 放在同样张表中,并收取延续数量超过3的

select if(count(id)>=3,count_concat(id),null)e from(
SELECT @newid:=@newid+1 AS newid,test.* ,@cha:=id-@newid AS cha 
FROM(SELECT @newid:=0)r, test WHERE people>100)
as d group by cha

5.将上步获得的表和主表 获得所供给的

SELECT id,DATE,people FROM test,
(SELECT IF (COUNT(id)>3,GROUP_CONCAT(id),NULL)e 
FROM (SELECT @newid:=@newid+1 AS newid,test.* ,@cha:=id-@newid AS cha 
FROM(SELECT @newid:=0)r, test WHERE people>100)AS d   GROUP BY cha ) AS f 
WHERE f.e IS NOT NULL AND FIND_IN_SET(id,f.e);

听讲还足以用存储进度来完结,但是自个儿没尝试,稍后尝试

以上

 

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,'电脑',0);//钦点插入的大器晚成大器晚成
INSERT INTO bookcategory VALUES(1,'Computer',0);//依据私下认可的插入
INSERT INTO bookcategory(category_id,category,parent_id) VALUES(1,'Computer',0),(2,'xxx',3)(3,'xxxxx',4);//同期插入多条数据
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让这一列自动安装编号,私下认可开始值为,最后为设置早先值为5
ALTER TABLE bookcategory MODIFY category_id INT AUTO_INCREMENT=X//为原来就有表增加自增列
ALTER TABLE bookcategory MODIFY category_id INT;//去掉自增列
//有外键关系的话增加自增,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);//增多外键
SELECT price FROM bookinfo WHERE book_id=201501;//查询book_id为二零一四01书的价格
SELECT * FROM readerinfo//查看读者新闻表
SELECT xxx,xxx,xxx FROM readerinfo//查询钦点列
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;//展现不重复的询问
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这么些表中的card_id为xxx的balance
DELETE FROM readerinfo WHERE card_id='二零一六31513133'//单表数据记录的去除,不加where则为全方位删减
TRUNCATE TABLE readerinfo;//删除原表再成立空表
SELECT COUNT(*) FROM readerinfo WHERE sex='男'//对查询结果的分组
SELECT sex FROM readerinfo GROUP BY sex;//查询有稍许种性别
SELECT sex COUNT(*) FROM readerinfo GROUP BY sex;//计算各样性其他食指
SELECT sex FROM readerinfo GROUP BY sex WHERE COUNT(sex)>3;//也足以加约束条件。总括每一种性其余食指
SELECT * FROM bookinfo O翼虎DE奥迪Q5 BY price//对查询结果排序,默以为升序
SELECT * FROM bookinfo O奥迪Q7DE大切诺基 BY price,store;//price相符的,根据仓库储存排序
SELECT * FROM bookinfo ORDER BY price ASC,store DESC;//asc升序,desc降序
SELECT * FROM bookinfo LIMIT 3;//limit节制查询数量,偏移量为0起先,展现前三行
SELECT * FROM bookinfo LIMIT 2,2;//展现第二条语句的后四个语句
SELECT store,COUNT(*) FROM bookinfo GROUP BY store O奥迪Q5DECRUISER BY store DESC LIMIT 4;//总计仓库储存个数,并降序排序,并查看前四条语句

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