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Add Foreign Key using ALTER TABLE. The following SQL command adds a Foreign Key to an existing table. ALTER TABLE Subject ADD FOREIGN KEY (StudentID) REFERENCES Student(StudentID); Drop foreign key MySQL. For dropping a Foreign key from a MySQL table, you need to know the name of the foreign key first.
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
ALTER TABLE child_table_name ADD FOREIGN KEY (child_table_column) REFERENCES parent_table_name(parent_table_column); child_table_name is that table in which we want to add constraint. child_table_column is that table column in which we want to add foreign key.
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.
8 kwi 2021 · Syntax –. ALTER TABLE table_name ADD FOREIGN KEY (column_name) REFERENCE table_name (Referencing column_name in table_name); Query –. ALTER TABLE exam ADD FOREIGN KEY (student_id) REFERENCES student (student_id);
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:
Here is the basic syntax of defining a foreign key constraint in the CREATE TABLE or ALTER TABLE statement: [CONSTRAINT constraint_name] FOREIGN KEY [foreign_key_name] (column_name, ...) REFERENCES parent_table(colunm_name,...) [ON DELETE reference_option] [ON UPDATE reference_option] Code language: SQL (Structured Query Language) (sql)
