What is the Default ON DELETE Behavior of Foreign Key Constraints in MySQL?

MySQL Foreign Key Constraints: Default ON DELETE Behavior Explained

When working with MySQL databases, managing foreign key constraints is essential to ensure data integrity. One of the fundamental aspects of foreign key relationships is the ON DELETE behavior, which determines what happens to the child rows when the corresponding parent row is deleted.

Default ON DELETE Behavior: Explained

By default, MySQL assigns the ON DELETE behavior as NO ACTION, which means that the deletion of the parent row is prohibited if it would break any foreign key relationships. In other words, the child rows must continue to reference a valid parent row.

Other ON DELETE Options

Besides the default behavior, there are four other ON DELETE options available:

• SET NULL: Nulls the foreign key column in the child table when the parent row is deleted. This is allowed only if the foreign key column is nullable.
• RESTRICT: This option is synonymous with NO ACTION, prohibiting the deletion of the parent row when it would affect the child rows.
• CASCADE: Automatically deletes all child rows that reference the deleted parent row.
• SET DEFAULT: This option is not supported in MySQL and should not be used.

Summary

To summarize, the default ON DELETE behavior in MySQL is NO ACTION/RESTRICT, which prevents the deletion of parent rows that would invalidate any foreign key constraints. Other options include SET NULL, CASCADE (to automatically delete child rows), and SET DEFAULT (not supported in MySQL).

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