If no default values available, MariaDB will raise an error.īy default, MariaDB uses the restrict option if you don’t specify either on delete or on update clauses. The foreign key columns will set to their default values if the columns in the parent table are updated or deleted. set default: only worked with obsolete PBXT storage engine.no action: has the same effect as restrict.restrict: if a row in the parent table has referencing rows in the child table, it cannot be updated or deleted.set null: when a row in the parent table is deleted or updated, the corresponding row in the child table is set to null.cacade: when a row in the parent table is deleted or updated, the corresponding row in the child table is automatically deleted or updated.I have two foreign keys in transactions table and thats way its not. The reference_option accepts one of the following five values with the corresponding effects: However I had tried to delete payment record in phpMyAdmin and cascading delete. The reference_option provides actions that MariaDB will take when values in the parent table are deleted ( on delete) and/or updated ( on update). Finally, determine how foreign key constraint maintains the referential integrity between the two tables using the on delete and on update clauses.Third, specify the parent table with a list of columns to which the foreign key columns reference after the references keyword.Second, specify the name of the foreign key followed by a list of comma-separated column names placed within parentheses.MariaDB will implicitly assign a generated name if you skip the constraint clause. First, specify the name of the foreign key constraint after the constraint keyword.The following illustrates the syntax of defining a foreign key constraint:Ĭode language: SQL (Structured Query Language) ( sql ) Typically, you define foreign key constraints for a table at the time of the table creation. To define a foreign key for a table, you use the foreign key constraint. In other words, a country will not exist without a region.Ī table can have multiple foreign keys that refer to the primary keys of different parent tables. ![]() The foreign key constraint prevents you from inserting a row into the countries table without a corresponding row in the regions table. The region_id in the countries table is the foreign key that references to the region_id column in the regions table.įor each row in the countries table, you can find a corresponding row in the regions table. See the following regions and countries table from the nation sample database: Typically, a foreign key column in a child table references to the primary key column of the parent table. What is a foreign keyĪ foreign key is a column or set of columns in a table that references a column or a set of columns in another table, which enforces the referential integrity between the two tables.Ī table that has the foreign key is called a child table while the table to which the foreign key references is known as a parent table. Summary: in this tutorial, you will learn how to use the MariaDB foreign key constraints to enforce the referential integrity between tables.
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