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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]
10 lip 2024 · There are 2 ways to create a FOREIGN KEY in MySQL: Using CREATE TABLE. Using ALTER TABLE. We can create a FOREIGN KEY while creating the table, or add a FOREIGN KEY after the creation of the table. Using CREATE TABLE Statement to Create FOREIGN KEY. CREATE method can be used to define your FOREIGN KEY in MYSQL in the following way:
The CREATE TABLE statement allows you to create a new table in a database. The following illustrates the basic syntax of the CREATE TABLE statement: CREATE TABLE [ IF NOT EXISTS ] table_name( column1 datatype constraints , column2 datatype constraints , ...
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:
In this tutorial, you have learned about the MySQL foreign key and how to create a foreign key constraint with various reference options.
Create the parent and child tables using the following SQL statements: CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ) ENGINE=INNODB; CREATE TABLE child ( id INT, parent_id INT, INDEX par_ind (parent_id), FOREIGN KEY (parent_id) REFERENCES parent(id) ) ENGINE=INNODB; Insert a row into the parent table, like this:
