约束以及修改数据表

来源：互联网发布：剑网3捏脸数据非法编辑：程序博客网时间：2024/04/27 22:42
mysql> alter table users1 drop truename,drop password,drop age;Query OK, 1 row affected (0.20 sec)Records: 1  Duplicates: 0  Warnings: 0

mysql> delete from provinces where id=3;Query OK, 1 row affected (0.06 sec)
mysql> select * from provinces;+----+-------+| id | pname |+----+-------+| 1 | A || 2 | B || 3 | C |+----+-------+3 rows in set (0.00 sec)

mysql> insert provinces(pname)values('A');Query OK, 1 row affected (0.05 sec)
mysql> create table users1( -> id smallint unsigned primary key auto_increment, -> username varchar(10) not null, -> pid smallint unsigned, -> foreign key (pid) references provinces(id) on delete cascade);Query OK, 0 rows affected (0.09 sec)

mysql> show indexes from provinces\G;*************************** 1. row *************************** Table: provinces Non_unique: 0 Key_name: PRIMARY Seq_in_index: 1 Column_name: id Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: Index_type: BTREE Comment:Index_comment:1 row in set (0.00 sec)ERROR:No query specified
mysql> create table users( -> id smallint unsigned primary key auto_increment, -> username varchar(10) not null, -> pid smallint unsigned, -> foreign key(pid) references provinces (id) -> );Query OK, 0 rows affected (0.12 sec)

mysql> create table provinces( -> id smallint unsigned primary key auto_increment, -> pname varchar(20)not null -> );Query OK, 0 rows affected (0.27 sec)mysql> show create table provinces;+-----------+--------------------------------------------------------------------------------------------------------------------------------+| Table | Create Table |+-----------+--------------------------------------------------------------------------------------------------------------------------------+| provinces | CREATE TABLE `provinces` ( `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `pname` varchar(20) NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 |+-----------+--------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)
阅读全文
0 0