Foreign keys can refer to another column in the same table. The top-level folder might need to be its own parent - I don't know if it'll let you have a NULL there.

H2 supports a syntax to safely drop constraint if it not exists i.e. drop constraint if exists fk_symbol.The similar syntax is used in MariaDB: drop foreign key if exists fk_symbol but the original ...

Hence, the birth of the MySQL InnoDB vs. MyISAM debate. Of course, MySQL users prior to the 5.5 release were probably perplexed by the assertion that the database didn't support foreign keys. MySQL ...

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