@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...
ALTERTABLEtable_nameDROPCONSTRAINTMyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTERTABLEtable_nameDROPINDEXMyUniqueConstraint; DROP PRIMARY KEY (删除主键),语法如下: ALTERTABLEtable_nameDROPCONSTRAINTMyPrimaryKey; 如果是 MYSQL ,代码是这样: ALTERTABLEtable_nameDROPPRIMARYKEY; TRUNCATE TABLE PostgreSQL 中...
DROP CONSTRAINT (删除约束),语法如下: ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint; 如果是 MYSQL ,代码是这样: ALTER TABLE table_name DROP INDEX MyUniqueConstraint; DROP PRIMARY KEY (删除主键),语法如下: ALTER TABLE table_name DROP CONSTRAINT MyPrimaryKey; ...
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. Example: How to Add Primary Key Constraint to a Column in PostgreSQL? The below snippet will let you understand how to...
ADD CONSTRAINT PostgreSQL ALTER TABLE example Let us consider the tablesorders. SQL Code: CREATE TABLE orders( ord_no integer PRIMARY KEY, ord_date date NOT NULL, cus_name character(25) NOT NULL, item_code integer NOT NULL, item_grade character(1)NOT NULL DEFAULT 'A', ...
在PostgreSQL中,ALTER TABLE命令用于修改现有表的结构。当对表进行大规模修改时,可能会导致ALTER TABLE执行变慢的情况。 Alter Table太慢可能由以下几个因素引起:...
ADD CONSTRAINT constraint_name constraint_type (column_name); ALTER TABLE table_name ENABLE/DISABLE TRIGGER trigger_name; 在PostgreSQL中,ALTER命令也提供了类似的功能,并且还允许重命名列: ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name; ...
The above command will add a “NOT NULL” constraint in the “emp_id” column: Let’s verify the table’s alteration using the following command: \demp_data; The “NOT NULL” constraint has been added to the emp_id column. Example 6:Dropping a Constraint ...
ERROR: duplicate key value violates unique constraint "unique_url" DETAIL: Key (url)=(https://neon.tech/postgresql/) already exists. The following statement changes the name of the links table to urls: ALTER TABLE links RENAME TO urls; In this tutorial, you have learned how to use the P...
PostgreSQL中对应的语法在alter table中,因为触发器与表相关,这样设计语法也符合逻辑的。 https://www.postgresql.org/docs/devel/static/sql-altertable.html ALTERTABLE[ IFEXISTS] [ONLY] name [*] action [, ... ] DISABLETRIGGER[ trigger_name|ALL|USER] ...