SQL> drop table t; drop table t * ERROR at line 1: ORA-02449: unique/primary keys in table referenced by foreign keys (违反了constraint,员工销售表t1有參照到table t,这个reference relation不允许你drop table t) SQL> drop table t cascade constraints; Table dropped. SQL> select * from t1; ...
Table dropped. SQL> drop table t1; Table dropped. SQL> create table t (id number,name varchar2(20)); Table created. SQL> create table t1 (id number,sal number); Table created. SQL> alter table t add constraint t_pk primary key (id); Table altered. SQL> alter table t1 add constra...
SQL> select CONSTRAINT_NAME,TABLE_NAME from dba_constraints where owner = 'SYS' and TABLE_NAME = 'B' no rows selected 我们可以发现利用Drop table cascade constraints可以刪除从表的constraint來达成你drop table t的目的,原來属于B的foreign key constraint已经跟随着被删除掉了,但是,储存在table B中的资...
SQL> drop table t; drop table t * ERROR at line 1: ORA-02449: unique/primary keys in table referenced by foreign keys (违反了constraint,员工销售表t1有參照到table t,这个reference relation不允许你drop table t) SQL> drop table t cascade constraints; ...
table_name Is the name of the table to be removed. Remarks DROP TABLE can't be used to drop a table that is referenced by a FOREIGN KEY constraint. The referencing FOREIGN KEY constraint or the referencing table must be dropped first. Multiple tables can be dropped in the same DROP TABLE...
SQL 复制 > CREATE TABLE persons(first_name STRING NOT NULL, last_name STRING NOT NULL, nickname STRING); > ALTER TABLE persons ADD CONSTRAINT persons_pk PRIMARY KEY(first_name, last_name); > CREATE TABLE pets(name STRING, owner_first_name STRING, owner_last_name STRING); >...
create table 表名称(字段1 数据类型 not null,字段2 数据类型 ,[constraint 自定义约束名称] unique(字段1,字段2)); 或 alter table 表名称 add [constraint 自定义约束名称] unique(字段1,字段2) 撤销unique 约束 适用mysql: alter table 表名称 drop index 字段 适用SQL Server / Oracle / MS Access: ...
truncate table 在功能上与不带 WHERE 子句的 delete语句相同:二者均删除表中的全部行。 但truncate 比 delete速度快,且使用的系统和事务日志资源少。 delete 语句每次删除一行,并在事务日志中为所删除的每行记录一项。所以可以对delete操作进行roll back
SQL> select CONSTRAINT_NAME,TABLE_NAME from dba_constraintswhere owner = 'SYS' and TABLE_NAME = 'B' ; no rows selected 利用Drop tablecascadeconstraints可以删除从表的constraint,从而可实现drop table A。原属于B的foreign key constraint已经跟随着被删除掉了,但是,储存在table B中的记录不会被删除,也...
SQL Server有两种类型的文件组:· 主文件组:包含主数据文件和任何没有明确分配给其他文件组的其他文件。系统表的所有页均分配在主文件组中。·用户定义文件组:用户定义文件组是通过在CREATE DATABASE或ALTER DATABASE语句中使用FILEGROUP关键字指定的任何文件组。