增加字段：使用`ALTER TABLE`命令搭配`ADD COLUMN`子句来新增字段。新字段对于表中已存在的行，默认填充为空值。同时可以在新增字段时定义约束，通过`CHECK`、`UNIQUE`、`FOREIGN KEY`等子句实现。新字段不能立即设置非空约束或默认值，因为这些特性尚未完全实现于现有行。但可以在后续操作中调整这些设置。
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, ...
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) REFERENCES t...
ALTER [ COLUMN ] column_name DROP EXPRESSION [ IF EXISTS ] ALTER [ COLUMN ] column_name ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] ALTER [ COLUMN ] column_name {SETGENERATED { ALWAYS | BY DEFAULT } |SETsequence_option | RESTART [ [ WITH ] restart ...
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, ...
ALTER TABLE products DROP COLUMN description; 3,增加约束 要增加一个约束,使用表约束语法。比如: 代码示例: ALTER TABLE products ADD CHECK (name <> ''); ALTER TABLE products ADD CONSTRAINT some_name UNIQUE (product_no); ALTER TABLE products ADD FOREIGN KEY (product_group_id) REFERENCES product_...
外键默认名称为 tablename_columnname_fkey "CONSTRAINT skills_Userid_fkey" 可省略。CREATE TABLE IF NOT EXISTS skills( Id serial, Userid integer NOT NULL, Name VARCHAR(10) NOT NULL, CreatedAt timestamptz DEFAULT current_timestamp, UpdatedAt timestamptz DEFAULT current_timestamp, CONSTRAINT skills_...
TABLE "employees" CONSTRAINT "emp_manager_fk" FOREIGN KEY (manager_id) REFERENCES employees(employee_id)增加字段增加字段使用ALTER TABLE ... ADD COLUMN语句:ALTER TABLE table_nameADD COLUMN column_name data_type column_constraint;添加字段与创建表时的字段选项相同,包含字段名称、字段类型以及可选的约束...
{ UNIQUE ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | PRIMARY KEY ( column_name [, ... ] ) [ USING INDEX TABLESPACE tablespace ] | CHECK ( expression ) | FOREIGN KEY ( column_name [, ... ] ) REFERENCES ref_table [ ( ref_column [, ... ] ) ] ...
ADD CONSTRAINT <foreign key constraint> FOREIGN KEY (<foreign_key_field>)REFERENCES <parent_table>(<primary key field>)...同样增加maintenance_work_mem配置参数也能提高重新创建外键约束的性能。暂停触发器 INSERT或DELETE触发器（如果导入过程还涉及从目标表中删除记录）可能会导致批量数据导入延迟。这是因为...