mysql> insert into student(name) values('xiaobai'); Query OK, 1 row affected (0.00 sec) mysql> select * from student; +---+---+---+ | id | name | sex | +---+---+---+ | 1 | xiaobai | male | +---+---+---+ row in set (0.00 sec) mysql> 对于自增的字段,在用de...
mysql>ALTERTABLEtestalter_tblENGINE=MYISAM;mysql>SHOWTABLESTATUSLIKE'testalter_tbl'\G***1.row***Name:testalter_tblType:MyISAMRow_format:FixedRows:0Avg_row_length:0Data_length:0Max_data_length:25769803775Index_length:1024Data_free:0Auto_increment:NULLCreate_time:2007-06-03 08:04:36Update_tim...
sql中constraint前缀的用意(PK、UK、DF、CK、FK) -- 主键 constraint PK_字段 primary key(字段), --唯一约束 constraint UK_字段 unique key(字段), -- 默认约束 constrint DF_字段 default('默认值') for 字段, --检查约束 constraint CK_字段 check(约束。如:len(字段)>1), -- 主外键关系 constrain...
..) reference_definition | ADD [CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED] | DROP {CHECK | CONSTRAINT} symbol | ALTER {CHECK | CONSTRAINT} symbol [NOT] ENFORCED | ALGORITHM [=] {DEFAULT | INSTANT | INPLACE | COPY} | ALTER [COLUMN] col_name { SET DEFAULT {literal | (...
ADDCONSTRAINTfk_customer FOREIGNKEY(customer_id) REFERENCEScustomers(customer_id); 7. 修改表名 ALTER TABLE old_table_name RENAME TO new_table_name; 以下SQL 语句将表名由 employees 修改为 staff: 实例 ALTERTABLEemployees RENAMETOstaff; 注意: ...
ADD CONSTRAINT constraint_name constraint_type (column_name); ALTER TABLE table_name ENABLE/DISABLE TRIGGER trigger_name; 在PostgreSQL中,ALTER命令也提供了类似的功能,并且还允许重命名列: ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name; ...
1. drop：删除数据库 drop语句将表所占用的空间全释放掉。drop > truncate > delete 方式1：如果要...
MySQL中添加外键约束的语句是()A、ALTER TABLE...ADD CONSTRAINT...FOREIGN KEY...REFERENCES...B、ADD CONSTRAINT...FOREIGN KEY...REFERENCES...C、ALTER TABLE...ADD CONSTRAINT...PRIMARY KEY...REFERENCES...D、ADD CONSTRAINT...PRIMARY KEY...REFERENCES......
See Section 1.6.2, “MySQL Differences from Standard SQL”. For ALTER TABLE, unlike CREATE TABLE, ADD FOREIGN KEY ignores index_name if given and uses an automatically generated foreign key name. As a workaround, include the CONSTRAINT clause to specify the foreign key name: ...
constraint_definition:约束的定义(如UNIQUE、PRIMARY KEY)。 示例: 向employees表中添加一个唯一约束: ALTERTABLEemployeesADDCONSTRAINTunique_emailUNIQUE(email); 6.2 删除约束 要从表中删除约束,可以使用以下语法: ALTERTABLEtable_nameDROPINDEX index_name; ...