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Foreign key on two fields
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Information générale
Forum:
Microsoft SQL Server
Catégorie:
Autre
Versions des environnements
SQL Server:
SQL Server 2005
Divers
Thread ID:
01520713
Message ID:
01520719
Vues:
28
>>Hi,
>>
>>Say I want to create a Foreign key constraint on two fields (one char and one smallint). In the parent table (where the combination of these two fields is unique) I will have a unique index on Char_field + SmallInt_fld.
>>
>>Do I need to have an index in the Child table (where the Foreign key constraint will be set) on these two fields (Char_field + SmallInt_fld) or two index keys, one for each field?
>>
>>The foreign key constrain will look something like this:
>>
>>
>>ALTER TABLE [dbo].[child_table] WITH CHECK ADD CONSTRAINT [FK_child_somename]
>>FOREIGN KEY([char_fld], [smallint_fld])
>>REFERENCES [dbo].[parent_table] ([char_fld], [smallint_fld])
>>ON UPDATE CASCADE
>>
>>
>>TIA.
>
>It should be one index per both fields. I suggest to make integer field first key and char the second in the list of fields.
>This is assuming you always use both fields in join conditions and select filters.

Sorry to bug you again with my silly questions. Why is it important that the Integer field is the first key and not the other way around?
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