UPDATE
table1 {[INNER]JOIN | {LEFT | RIGHT}[OUTER]JOIN} table2                                                                                                                                                                                                            
ON conditional_ expr 
SET col1 = {expr1 | DEFAULT}
[,col2={expr2 | DEFAUL}]...
[WHERE where_ condition]

/*
今天身份证号为210210199901012222的读者将超限的图书20151101归还，根据描述实现如下需求：
1、更新借阅信息表，将借阅状态（status）更新为‘是’。
2、更新罚款记录信息表，更新实际还书日期和罚款金额，罚款金额为每超出一天扣0.2元。
3、同时更新读者信息表的余额。（在余额中扣除罚款金额）
*/

UPDATE readerfee t1
JOIN readerinfo t2 ON t1.card_id = t2.card_id
SET actual_return_date = sysdate(),
 book_fee = datediff(sysdate(), return_date) * 0.2,
 balance = balance - book_fee
WHERE
    t1.book_id = 20151101
AND t1.card_id = ‘210210199901012222‘;

DELETE table1[.*], table2[.*]

FROM table1 {[INNER]JOIN | {LEFT| RIGHT}[OUTER]JOIN} table2 ON conditional_ expr

[WHERE where_ condition]

-- 1、由于业务需求，需要删除图书类别表中在图书信息表中没有图书记录的类别。
SELECT
    book_id,
    book_name,
    category
FROM
    bookcategory_bak t1
LEFT JOIN bookinfo_bak t2 ON t1.category_id = t2.book_category_id
WHERE
    parent_id <> 0;

DELETE t1
FROM
    bookcategory_bak t1
LEFT JOIN bookinfo_bak t2 ON t1.category_id = t2.book_category_id
WHERE
    parent_id <> 0
AND book_id IS NULL;

SELECT
    *
FROM
    bookcategory_bak;

-- 2、需要删除图书类别表的编程语言的类别，以及图书信息表中关于编程语言的图书记录。
SELECT
    book_id,
    book_name,
    category_id,
    category
FROM
    bookcategory_bak t1
INNER JOIN bookinfo_bak t2 ON t1.category_id = t2.book_category_id;

DELETE t1,
 t2
FROM
    bookcategory_bak t1
INNER JOIN bookinfo_bak t2 ON t1.category_id = t2.book_category_id
WHERE
    t1.category_id = 3;

CREATE TABLE table1_bak
AS
SELECT *
FROM table1;

insert into table1 select * from table1_bak;

insert into table1(字段1，字段2） select 字段m,字段n from  table2;