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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.
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.
14 paź 2008 · SELECT CONSTRAINT_NAME, TABLE_NAME, REFERENCED_TABLE_NAME FROM information_schema.REFERENTIAL_CONSTRAINTS WHERE CONSTRAINT_SCHEMA = '<schema>' AND TABLE_NAME = '<table>' for foreign keys from <table>, or
MySQL supports foreign key references between one column and another within a table. (A column cannot have a foreign key reference to itself.) In these cases, a “child table record” refers to a dependent record within the same table.
10.3.4 Foreign Key Optimization. If a table has many columns, and you query many different combinations of columns, it might be efficient to split the less-frequently used data into separate tables with a few columns each, and relate them back to the main table by duplicating the numeric ID column from the main table. That way, each small table ...
Summary: in this tutorial, you will learn about MySQL foreign key and how to create, drop, and disable a foreign key constraint. Introduction to MySQL foreign key. 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.
To add a foreign key, select Table Designer , Relationships... from the main menu. This displays the Foreign Key Relationship dialog. Click Add. You can then set the foreign key name, referenced table name, foreign key columns, and actions upon update and delete.
