The SQL DROP FOREIGN KEY clause is the SQL clause that removes an entire SQL foreign key from a table. It is a clause of the SQL ALTER TABLE statement.
You may drop a foreign key permanently when it is no longer useful or temporarily. If the foreign key is harming performance or not helping referential integrity it could be dropped.
Foreign keys may slow down the loading of data because they must be validated during the data load process. For high performance loads, a foreign key could be dropped for the duration of a load and then recreated.
Before dropping a table, it may be necessary to drop foreign keys refering to that table.
The SQL DROP FOREIGN KEY command is used as follows.
SQL DROP FOREIGN KEY Clause Syntax
ALTER TABLE <table_name>
DROP FOREIGN KEY <foreignkey_name>
SQL DROP FOREIGN KEY Statement Example
The following example drops a foreign key named FK_SALES_ORDER_LINE_PRODUCT on a table named SALES_ORDER_LINE.
ALTER TABLE SALES_ORDER_LINE
DROP FOREIGN KEY FK_SALES_ORDER_LINE_PRODUCT