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The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
Following is the basic syntax of defining a foreign key constraint in CREATE TABLE and ALTER TABLE constraint in MySQL. [CONSTRAINT constraint_name] FOREIGN KEY [foreign_key_name] (col_name, ...) REFERENCES parent_tbl_name (col_name,...) [ON DELETE reference_option] [ON UPDATE reference_option]
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 FOREIGN KEY constraint is a key used to link two tables together. A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
5.6.6 Using Foreign Keys. MySQL supports foreign keys, which permit cross-referencing related data across tables, and foreign key constraints, which help keep the related data consistent. A foreign key relationship involves a parent table that holds the initial column values, and a child table with column values that reference the parent column ...
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 foreign key places constraints on data in the related tables, which allows MySQL to maintain referential integrity. Let’s take a look at the following customers and orders tables from the sample database.
A foreign key is defined here: After the CONSTRAINT keyword fk_city_country is the name of the foreign key. It is optional. Following the FOREIGN KEY keyword is the column name that is the foreign key. Following the REFERENCES keyword are the referenced tables and columns.
