ALTER TABLE table_name DROP COLUMN column_name; 修改表中某列的 DATA TYPE(数据类型),语法如下: ALTER TABLE table_name ALTER COLUMN column_name TYPE datatype; 给表中某列添加 NOT NULL 约束,语法如下: ALTER TABLE table_name ALTER column_name datatype NOT NULL; 给表中某列 ADD UNIQUE CONSTRAINT...
alter table tablename modify columnname datatype not null; 5给表中某列 ADD UNIQUE CONSTRAINT( 添加 UNIQUE 约束),语法如下: alter table tablename add constraint myuniquecontraint unique(column1,column2...); 6给表中 ADD CHECK CONSTRAINT(添加 CHECK 约束),语法如下: alter table tablename add cons...
ALTERTABLEemployees RENAMECOLUMNmiddle_nameTOsecond_name; 6. 添加和删除约束 6.1 添加约束 要向表中添加约束,可以使用以下语法: ALTERTABLEtable_nameADDCONSTRAINTconstraint_name constraint_definition; 示例: 向employees表中添加一个唯一约束: ALTERTABLEemployeesADDCONSTRAINTunique_emailUNIQUE(email); 6.2 删除约束...
Postgres on Neon comes with instant point-in-time recovery. Get the free plan here. Summary: in this tutorial, you will learn how to use the PostgreSQL ALTER TABLE statement to modify the structure of a table. Introduction to PostgreSQL ALTER TABLE statement To change the structure of an ...
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_...
ADD table_constraint This form adds a constraint to a table. For details, seeCREATE TABLE. DROP CONSTRAINT This form drops constraints on a table. Currently, constraints on tables don't need unique names, so there might be more than one constraint matching the specified name. All...
How to ADD a PRIMARY KEY Constraint Using the ALTER TABLE Command? PostgreSQLallows us to add or drop a constraint using theALTER TABLEcommand, such as adding or dropping a unique constraint, primary key constraint, not null constraint, etc. ...
psql postgres -c "ALTER TABLE journal ALTER ekeyword TYPE character(350)" 好了,修改结束。 附ALTER语句的文档。 --- Name ALTER TABLE -- 修改表的定义 Synopsis ALTER TABLE [ ONLY ]name[ * ]action[, ... ] ALTER TABLE [ ONLY ]name[ ...
1 [ALTER TABLE CONTENT add constraint fk6382c05917d4a070 foreign key (PREVVER) references CONTENT(CONTENTID)]; SQL state [55006]; error code [0]; ERROR: cannot ALTER TABLE "content" because it has pending trigger events; nested exception is...
[ IF EXISTS ] table_name ADD ( { column_name data_type [ compress_mode ] [ COLLATE collation ] [ column_constraint [ ... ] ] } [, ... ] ); ALTER TABLE [ OFFLINE | [ ONLINE [ WITH ( { online_parameter = value } [, ... ] ) ] ] ] [ IF EXISTS ] table_name MODIFY ...