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31 lines
901 B
Markdown
31 lines
901 B
Markdown
# Add ON DELETE CASCADE To Foreign Key Constraint
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The `alter table` command lets you do quite a bit. But when it comes to
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altering existing constraints, there is not much you can do. If you want to
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add an `on delete cascade` to an existing foreign key constraint, you are
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going to need two statements.
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The first statement will drop the constraint and the second statement will
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recreate it with the addition of the `on delete` clause. Furthermore, you'll
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want to do this in a transaction to ensure the integrity of your data during
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the transition between indexes.
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Here is an example:
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```sql
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begin;
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alter table orders
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drop constraint orders_customer_id_fkey;
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alter table orders
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add constraint orders_customer_id_fkey
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foreign key (customer_id)
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references customers (id)
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on delete cascade;
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commit;
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```
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[source](http://stackoverflow.com/questions/10356484/how-to-add-on-delete-cascade-constraints)
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