CREATE TABLE orders ( order_id integer PRIMARY KEY, product_no integer REFERENCES products, quantity integer ); # 定义多个 Column 组成的外键,要求被约束列(外键)的数量和类型应该匹配被引用列(主键)的数量和类型。 CREATE TABLE t1 ( a integer PRIMARY KEY, b integer, c integer, FOREIGN KEY (b, ...
```sql CREATE TABLE table1 ( id SERIAL PRIMARY KEY, column1 VARCHAR(50), column2 INTEGER, FOREIGN KEY (column2) REFERENCES table2(id) ); ``` 2、如果表已经创建,可以使用ALTER TABLE语句添加外键约束,如下所示: ```sql ALTER TABLE table1 ADD CONSTRAINT fk_column2 FOREIGN KEY (column2) RE...
--添加主键 alter table cities add PRIMARY KEY(name); --添加外键 alter table weather add FOREIGN key(city) REFERENCES cities(name) on update CASCADE on DELETE CASCADE; on update cascade: 被引用行更新时,引用行自动更新; on update restrict: 被引用的行禁止更新; on delete cascade: 被引用行删除...
cvarchar);altertabletbl_foreign_refdaddconstraintpk_tbl_foreign_refd_a_bprimarykey(a,b);createtabletbl_foreign( aint, bint, cvarchar);altertabletbl_foreignaddconstraintfk_tbl_foreign_a_bforeignkey(a,b)referencestbl_foreign_refd(a,b); 上表中完整外键其实如下,因为match,on delete,on update会...
PostgreSQL Alter Table Exercises: Write a SQL statement to add a foreign key constraint named fk_job_id on job_id column of job_history table referencing to the primary key job_id of jobs table.
addconstraint字段名 unique(字段名) --外键约束: altertable表名 addconstraint字段名--"FK"为外键的缩写 foreignkey (字段名)references关联的表名(关联的字段名)--注意'关联的表名'和'关联的字段名' altertable表A add constraint FK_B foreign key (ticket_no)references表B(ticket_no) ...
-- alter table 从表 add [constraint] [外键名称] foreign key (从表外键字段名) references 主表 (主表的主键); 实例: Alter table stuinfo add constraint fk_stuno foreign key(stuno) references student(stuno); 1. 2. 3. 4. 5. 6. ...
CREATE TABLE orders ( order_id integer PRIMARY KEY, product_no integer, quantity integer ); 给订单表增加外键: alter table orders add constraint orders_product_no_fkey foreign key ("product_no") references products("product_no"); 删除外键约束 如果要删除外键约束,则可以执行以下命令: alter table...
主要针对VACUUM,CREATE INDEX,ALTER TABLE ADD FOREIGN KEY等操作。 在对整个数据库进行VACUUM或者较大的index进行重建时,适当的调整该参数非常必要。 PostreSQL文档提示在启用了autoacuum功能的情况下,该参数不能配置的过大。 四.SGA内存 shared_buffers ---共享缓冲区 ...
To add a foreign key constraint to the existing table, you use the following form of the ALTER TABLE statement: ALTER TABLE child_table ADD CONSTRAINT constraint_name FOREIGN KEY (fk_columns) REFERENCES parent_table (parent_key_columns); When adding a foreign key constraint with ON DELETE CASC...