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+# 作业
+
+## 第二题
+
+CREATE DATABASE test01_market use test01_market CREATE TABLE customers( c_num int(11), c_name varchar(50), c_contact varchar(50), c_city varchar(50), c_birth date ); -- 要求3：将c_contact字段移动到c_birth字段后面 alter table customers MODIFY c_contact VARCHAR(50) AFTER c_birth; -- 要求4：将c_name字段数据类型改为 varchar(70) ALTER TABLE customers MODIFY c_name varchar(70); -- 要求5：将c_contact字段改名为c_phone ALTER TABLE customers CHANGE c_contact c_phone VARCHAR(50); -- 要求6：增加c_gender字段到c_name后面，数据类型为char(1) ALTER TABLE customers ADD c_gender char(1) AFTER c_name; -- 要求7：将表名改为customers_info ALTER TABLE customers RENAME TO customers_info; -- 要求8：删除字段c_city ALTER TABLE customers_info DROP c_city;
+
+## 第三题
+
+CREATE DATABASE test02_library use test02_library CREATE TABLE books( b_id INT(11) NOT NULL UNIQUE, b_name VARCHAR(50) NOT NULL, authors VARCHAR(100) NOT NULL, price FLOAT NOT NULL, pubdate year NOT NULL, note VARCHAR(100) NULL, num int(11) NOT NULL ); INSERT INTO books (b_id,b_name,authors,price,pubdate,note,num) VALUES (1,'talofaaa','dickes',23,'1995','novel',11); INSERT INTO books VALUES(2,'EmmaT','Jane lura',35,'1993','joke',22); INSERT INTO books VALUES(3,'Story of Jane','Jane Tim',40,'2001','novel',0); INSERT INTO books VALUES(4,'Lovey Day','George Byron',20,'2005','novel',30); INSERT INTO books VALUES(5,'Old land','Honore Blade',30,'2010','law',0); INSERT INTO books VALUES(6,'The Battle','Upton Sara',30,'1999','medicine',40); INSERT INTO books VALUES(7,'Rose Hood','Richard haggard',28,'2008','cartoon',28); UPDATE books set price=price+5 WHERE note='novel'; UPDATE books SET price=40 WHERE b_name='EmmaT'; DELETE from books where num=0;
+CREATE DATABASE test03_bookstore use test03_bookstore CREATE TABLE book( id int(11) NO NULL, title varchar(100) NO NULL, author varchar(100) NO NULL, price double(11,2) NO NULL, sales int(11) NO NULL, stockint(11) NO NULL, img_path varchar(100) NO NULL ); INSERT INTO book VALUES (1,'解忧杂货店','东野圭吾',27.2,102,98,'upload/books/解忧杂货店.jpg'),(2,'边城','沈从文',23.00,102,98,'upload/books/边城.jpg') CREATE TABLE users( id int(11) uner
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