Hello there! I use Firebird 2.1, but this question is not specific to
FB, I think

Basically, I have a table with a field which can "point" to two tables
(one or other, but *never* to both)

What the experts says about this scenario?

Option 1) is better to have a field which represent at what table I'm
pointing and then the ID field... ?

Option 2) or just two ID fields (FK to each table) and just leave null
the field I not use...

I hope I'm clear with my question!!

here it is a simple case (not a real one) of what I'm asking.



PURCHASE_INVOICES
==============
ID INTEGER,
DESCRPTION VARCHAR(100)

--

STOCK_MOVEMENTS
=============
ID INTEGER,
DESCRPTION VARCHAR(100)

--

Option 1)

ARTICLES
======
ID INTEGER,
DESCRPTION VARCHAR(100),
LAST_IN_TABLE CHAR(1)
LAST_IN_ID INTEGER

Option 2)

ARTICLES
======
ID INTEGER,
DESCRPTION VARCHAR(100),
ID_PURCHASE_INVOICES INTEGER (FK TO TABLE PURCHASE_INVOICES)
ID_STOCK_MOVEMENTS INTEGER (FK TO TABLE STOCK_MOVEMENTS)





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