MySQL如何增加表和给表字段赋值 本页介绍MySQL如何进行增加表和给表字段赋值的操作。 MySQL增加表和给表字段赋值 MySQL数据库对增加表和给表字段赋值的操作提供了以下几种方式: 增加表和表结构 CREATE TABLE tianyiyun ( uid MEDIUMINT NOT NULL AUTOINCREMENT, user CHAR(10) NOT NULL, PRIMARY KEY (uid) ); 1.不对新增字段赋值,数据库会自动赋值到字段中。 mysql> INSERT INTO tianyiyun (user) VALUES ('a'),('b'),('c'),('d'),('e'),('f'); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> select from tianyiyun; ++ uid user ++ 1 a 2 b 3 c 4 d 5 e 6 f ++ 6 rows in set (0.00 sec) mysql> show create table tianyiyun; ++ Table Create Table ++ tianyiyun CREATE TABLE tianyiyun ( uid mediumint(9) NOT NULL AUTOINCREMENT, user char(10) COLLATE utf8mb4bin NOT NULL, PRIMARY KEY (uid) ) ENGINEInnoDB AUTOINCREMENT7 DEFAULT CHARSETutf8mb4 COLLATEutf8mb4bin ++ 1 row in set (0.00 sec) mysql> 2.新增字段赋值0或者null,数据库会将新增的值填写到字段中。 mysql> INSERT INTO tianyiyun (uid,user) VALUES(0,'g'); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO tianyiyun (uid,user) VALUES(NULL,'h'); Query OK, 1 row affected (0.00 sec) mysql> select from tianyiyun; ++ uid user ++ 1 a 2 b 3 c 4 d 5 e 6 f 7 g 8 h ++ 8 rows in set (0.00 sec) mysql> show create table tianyiyun; ++ Table Create Table ++ tianyiyun CREATE TABLE tianyiyun ( uid mediumint(9) NOT NULL AUTOINCREMENT, user char(10) COLLATE utf8mb4bin NOT NULL, PRIMARY KEY (uid) ) ENGINEInnoDB AUTOINCREMENT9 DEFAULT CHARSETutf8mb4 COLLATEutf8mb4bin ++ 1 row in set (0.00 sec) 3.使用大于AUTOINCREMENT的值,数据库会将AUTOINCREMEN的值增加,该值也会新增到字段里面。 mysql> INSERT INTO tianyiyun (uid,user) VALUES(99,'i'); Query OK, 1 row affected (0.00 sec) mysql> select from tianyiyun; ++ uid user ++ 1 a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 99 i ++ 9 rows in set (0.00 sec) mysql> show create table tianyiyun; ++ Table Create Table ++ tianyiyun CREATE TABLE tianyiyun ( uid mediumint(9) NOT NULL AUTOINCREMENT, user char(10) COLLATE utf8mb4bin NOT NULL, PRIMARY KEY (uid) ) ENGINEInnoDB AUTOINCREMENT100 DEFAULT CHARSETutf8mb4 COLLATEutf8mb4bin ++ 1 row in set (0.00 sec) 4.使用小于AUTOINCREMENT的值,不会影响到数据插入。 mysql> INSERT INTO tianyiyun (uid,user) VALUES(30,'j'); Query OK, 1 row affected (0.00 sec) mysql> select from tianyiyun; ++ uid user ++ 1 a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 30 j 99 i ++ 10 rows in set (0.00 sec) mysql> show create table tianyiyun; ++ Table Create Table ++ tianyiyun CREATE TABLE tianyiyun ( uid mediumint(9) NOT NULL AUTOINCREMENT, user char(10) COLLATE utf8mb4bin NOT NULL, PRIMARY KEY (uid) ) ENGINEInnoDB AUTOINCREMENT100 DEFAULT CHARSETutf8mb4 COLLATEutf8mb4bin ++ 1 row in set (0.00 sec) 5.使用负值,数据也能正常插入。 mysql> INSERT INTO tianyiyun (uid,user) VALUES(30,'k'); Query OK, 1 row affected (0.00 sec) mysql> select from tianyiyun; ++ uid user ++ 30 k 1 a 2 b 3 c 4 d 5 e 6 f 7 g 8 h 30 j 99 i ++ 11 rows in set (0.00 sec) mysql> show create table tianyiyun; ++ Table Create Table ++ tianyiyun CREATE TABLE tianyiyun ( uid mediumint(9) NOT NULL AUTOINCREMENT, user char(10) COLLATE utf8mb4bin NOT NULL, PRIMARY KEY (uid) ) ENGINEInnoDB AUTOINCREMENT100 DEFAULT CHARSETutf8mb4 COLLATEutf8mb4bin ++ 1 row in set (0.00 sec)