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...
@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 TABLE table_name MODIFY column_name datatype NOT NULL; 给表中某列 ADD UNIQUE CONSTRAINT( 添加 UNIQUE 约束),语法如下: ALTER TABLE table_name ADD CONSTRAINTMyUniqueConstraintUNIQUE(column1,column2...); 给表中 ADD CHECK CONSTRAINT(添加 CHECK 约束),语法如下: ALTER TABLE table_name ADD CON...
ALTER TABLE table_name MODIFY column_name datatype NOT NULL; 给表中某列 ADD UNIQUE CONSTRAINT( 添加 UNIQUE 约束),语法如下: ALTER TABLE table_name ADD CONSTRAINT MyUniqueConstraint UNIQUE(column1, column2...); 给表中 ADD CHECK CONSTRAINT(添加 CHECK 约束),语法如下: ALTER TABLE table_name ADD...
The below snippet will let you understand how to add the“PRIMARY KEY”constraint in“PostgreSQL”using the“ALTER TABLE”command: ALTER TABLE team_info ADD PRIMARY KEY (team_rating); The output verified that multiple primary keys in the table“team_info”are not allowed. This is how you can...
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; ...
Add unique key constraint to table How to add unique key constraint to an existing table. Constraint syntax and example. Syntax ALTER TABLE table_name ADD CONSTRAINT key_name UNIQUE (column_name); Example ALTER TABLE users ADD CONSTRAINT uk_mail UNIQUE (usermail);...
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', ...
To drop a check constraint from a table in PostgreSQL, you can use the ALTER TABLE statement. The ALTER TABLE statement is used to modify the structure of an existing table in the database. Here’s the syntax to drop a check constraint from a table: ...
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: \d emp_data; The “NOT NULL” constraint has been added to the emp_id column. Example 6:Dropping a Constraint ...