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Re: Number of foreign keys

From: Tony Andrews <andrewst_at_onetel.com>
Date: 2 Dec 2004 03:20:07 -0800
Message-ID: <1101986407.019023.204010@f14g2000cwb.googlegroups.com>


Vinodh Kumar P wrote:
> I understand the number of foreign keys allowed is restricted by the
DBMS I
> use.
> In a general relational schema design perspective how many foreign
keys a
> table shall have?

Precisely as many as it requires - no more, no less. If that is more than your DBMS allows then you have an issue.

> If I have large number of foreign keys what anamolies it will lead
to?
None. It is the LACK of required foreign keys that will lead to anomalies.

> Is this crucial to identify all the foriegn key relationships for a
table?
Yes

Having said all that, if you find yourself designing a table that needs 100s of foreign keys, many of them referencing the same parent table, then it is quite likely that your design isn't good. For example this is a bad design:

CREATE TABLE department
( deptno INT PRIMARY KEY

, empno1 REREFENCES employee
, empno2 REREFENCES employee
, empno3 REREFENCES employee
, empno4 REREFENCES employee
, empno5 REREFENCES employee
, empno6 REREFENCES employee
, empno7 REREFENCES employee
, empno8 REREFENCES employee
, empno9 REREFENCES employee

...
); Received on Thu Dec 02 2004 - 05:20:07 CST

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