标签：category 多表 查询 book MySql bookinfo WHERE id SELECT

一、子查询

例子：更新借阅book_id为20190701图书的用户130429199007025628所剩下的余额

UPDATE readerinfo SET balance=balance-(SELECT price FROM bookinfo WHERE book_id=20190701)*0.05 WHERE card_id='130429199007025628'

1、使用比较运算符的子查询

（1）查询图书名称为软件测试的借阅信息

SELECT book_id FROM bookinfo WHERE book_name="软件测试";
SELECT * FROM borrowinfo WHERE book_id=(SELECT book_id FROM bookinfo WHERE book_name="软件测试")

（2）查询图书价格小于图书平均价格的图书信息

SELECT AVG(price) FROM bookinfo
SELECT * FROM bookinfo WHERE price<(SELECT ROUND(AVG(price),2) FROM bookinfo);

（3）查询图书类别不等于计算机的图书信息

SELECT category_id FROM bookcategory WHERE category!='计算机';
SELECT * FROM bookinfo WHERE book_category_id !=(SELECT category_id FROM bookcategory WHERE category='计算机')

（4）关键字any=some  all

查询图书类别属于计算机的图书信息

SELECT * FROM bookinfo WHERE book_category_id = ANY(SELECT category_id FROM bookcategory WHERE parent_id=1)

some和any是大于子查询的最小值

SELECT * FROM bookinfo WHERE price > ANY(SELECT price FROM bookinfo WHERE book_category_id=1)

all是大于子查询的最大值
SELECT * FROM bookinfo WHERE price > ALL(SELECT price FROM bookinfo WHERE book_category_id=1)

2、使用【not】in和exist的子查询

in=any

SELECT * FROM bookinfo WHERE book_category_id IN(SELECT category_id FROM bookcategory WHERE parent_id=1)

SELECT * FROM bookinfo WHERE book_category_id =ANY(SELECT category_id FROM bookcategory WHERE parent_id=1)

SELECT * FROM bookinfo WHERE book_category_id NOT IN(SELECT category_id FROM bookcategory WHERE parent_id=1)

子查询存在再执行外查询，不存在则外查询返回空

SELECT * FROM bookinfo WHERE EXISTS(SELECT category_id FROM bookcategory WHERE category='计算机')

SELECT * FROM bookinfo WHERE EXISTS(SELECT category_id FROM bookcategory WHERE category='不存在')

3、插入记录时使用子查询

INSERT INTO readerfee (book_id, card_id, return_date)
SELECT
book_id,
card_id,
return_date
FROM
borrowinfo
WHERE DATEDIFF(SYSDATE(), return_date) > 0
AND STATUS = "否" ;   插入查询的内容

二、多表连接查询

内连接，分析互相关联的三张表，只有借阅表与其他两个表内连接

SELECT borrowinfo.book_id,book_name,borrowinfo.card_id,NAME,tel,return_date,STATUS FROM borrowinfo
INNER JOIN bookinfo ON borrowinfo.book_id=bookinfo.book_id
INNER JOIN readerinfo ON borrowinfo.card_id=readerinfo.card_id
WHERE borrowinfo.STATUS="否";

可以简化为：表别名，inner省略

SELECT t1.book_id,book_name,t1.card_id,NAME,tel,return_date,STATUS FROM borrowinfo t1
JOIN bookinfo t2 ON t1.book_id=t2.book_id
JOIN readerinfo t3 ON t1.card_id=t3.card_id
WHERE t1.status="否";

2、外连接

SELECT book_id,book_name,category FROM bookcategory
LEFT JOIN bookinfo ON bookcategory.category_id = bookinfo.book_category_id
WHERE parent_id!=0;      左连接

SELECT book_id,book_name,category FROM bookinfo
RIGHT JOIN bookcategory ON bookcategory.category_id = bookinfo.book_category_id;    右连接

3、自连接      两张表为同一张表

SELECT a.category_id,a.category,s.category FROM bookcategory a   
LEFT JOIN bookcategory s
ON a.parent_id=s.category_id;    左和右连接是合并，会出现空的情况

SELECT a.category_id,a.category,s.category FROM bookcategory a   
INNER JOIN bookcategory s
ON a.parent_id=s.category_id;      内连接数据一一对应

4、多表更新

UPDATE readerfee t1 JOIN readerinfo t2 ON t1.card_id=t2.card_id
SET actual_date=SYSDATE(),book_fee=DATEDIFF(SYSDATE(),return_date)*0.2,balance=balance-book_fee
WHERE t1.book_id=20090101 AND t1.card_id="130429199007023333" 

5、多表删除

单表

SELECT book_id,book_name,category FROM bookcategory
LEFT JOIN bookinfo ON bookcategory.category_id=bookinfo.book_category_id
WHERE parent_id!=0;   先查询

DELETE bookcategory FROM bookcategory
LEFT JOIN bookinfo ON bookcategory.category_id=bookinfo.book_category_id
WHERE parent_id!=0 AND book_id IS NULL;   再删除

多表：

SELECT book_id,book_name,category_id,category FROM bookcategory
INNER JOIN bookinfo ON bookcategory.category_id=bookinfo.book_category_id
WHERE category_id=3

DELETE bookcategory,bookinfo FROM bookcategory
INNER JOIN bookinfo ON bookcategory.category_id=bookinfo.book_category_id
WHERE category_id=3

标签：category,多表,查询,book,MySql,bookinfo,WHERE,id,SELECT
来源： https://www.cnblogs.com/avril-xiao/p/13262723.html

本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享；
2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关；
3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关；
4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除；
5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。