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To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax: ALTER TABLE Orders ADD CONSTRAINT FK_PersonOrder
To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access: ALTER TABLE Orders. ADD CONSTRAINT FK_PersonOrder.
15 mar 2011 · Delete the key in the first one using an ALTER TABLE DROP FOREIGN KEY. Re-create it with the new columns in the second, using an ALTER TABLE ADD CONSTRAINT FOREIGN KEY. You can encapsulate both within a single transaction to make an atomic modification.
SQL FOREIGN KEY on ALTER TABLE. To create a FOREIGN KEY constraint on the "PersonID" column when the "Orders" table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access:
Summary: in this tutorial, you will learn about MySQL foreign key and how to create, drop, and disable a foreign key constraint. Introduction to MySQL foreign key. A foreign key is a column or group of columns in a table that links to a column or group of columns in another table.
The essential syntax for a defining a foreign key constraint in a CREATE TABLE or ALTER TABLE statement includes the following: [CONSTRAINT [symbol]] FOREIGN KEY. [index_name] (col_name, ...) REFERENCES tbl_name (col_name,...) [ON DELETE reference_option] [ON UPDATE reference_option] reference_option:
The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. The ALTER TABLE statement is also used to add and drop various constraints on an existing table. ALTER TABLE - ADD Column. To add a column in a table, use the following syntax: ALTER TABLE table_name. ADD column_name datatype;
