@文心快码postgresql alter table add constraint 文心快码 在PostgreSQL中,ALTER TABLE语句用于修改现有表的结构,例如添加或删除列、添加或删除约束等。下面是对你问题的详细回答: ALTER TABLE语句的用途: ALTER TABLE语句在PostgreSQL中用于修改已存在的表的结构。这包括添加或删除列、修改列的数据类型、添加或删除约束...
ALTER[COLUMN]columnTYPE type [ USING expression ] ALTER[COLUMN]columnSETDEFAULTexpression ALTER[COLUMN]columnDROPDEFAULT ALTER[COLUMN]column{SET|DROP}NOTNULL ALTER[COLUMN]columnSETSTATISTICSinteger ALTER[COLUMN]columnSETSTORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN } ADDtable_constraint DROPCONSTRAINTconst...
ALTER TABLE [ ONLY ] name [ * ] action [, ... ] ALTER TABLE [ ONLY ] name [ * ] RENAME [ COLUMN ] column TO new_column ALTER TABLE name RENAME TO new_name 其中action 可以是以选项之一: ADD [ COLUMN ] column_type [ column_constraint [ ... ] ] DROP [ COLUMN ] column [ RE...
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 [ ONLY ] name [ * ] RENAME [ COLUMN ] column TO new_column ALTER TABLE name RENAME TO new_name ALTER TABLE name SET SCHEMA new_schema 这里action 是下列之一: ADD [ COLUMN ] column type [ column_constraint [ ... ] ] ...
CREATE TABLE measurement_y2008m02 (LIKE measurement INCLUDING DEFAULTS INCLUDING CONSTRAINTS) TABLESPACE fasttablespace; ALTER TABLE measurement_y2008m02 ADD CONSTRAINT y2008m02 CHECK ( logdate >= DATE '2008-02-01' AND logdate < DATE '2008-03-01' ); ...
ALTER DOMAIN name { SET | DROP } NOT NULL ALTER DOMAIN name ADD domain_constraint ALTER DOMAIN name DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ] ALTER DOMAIN name OWNER TO new_owner 1. 2. 3. 4. 5. ALTER FUNCTION 修改一个函数的定义。
ALTER TABLE table_name ALTER COLUMN column_name [SET DEFAULT value | DROP DEFAULT]; To change the NOT NULL constraint, you use ALTER TABLE ALTER COLUMN statement: ALTER TABLE table_name ALTER COLUMN column_name [SET NOT NULL| DROP NOT NULL]; To add a CHECK constraint, you use ALTER TABL...
ALTERTABLEtestALTERCOLUMNpuzzleTYPEtext;ALTERTABLEtestADDCONSTRAINTchecksum_lengthCHECK(LENGTH(puzzle)<=32);我们先看看这个方法合适吗,这个方法当然合适,字段的扩充可以换个思路,我们可以给的无限,然后后面通过约束限制一下,这样DBA和开发其实都开心 当然也有人说,你加完约束,系统的性能会受到影响,来来来我们做一个...
constraint t_user_pk primary key (id) ); insert into t_user values(1, 'ACGkaka'); 会话一: 执行update语句。 begin; update t_user set username='ACGkaka1' where id=1; 会话二: 执行alter table语句,这时会处于等待状态。 alter table t_user add dept_no int; ...