Hi,

create a constraint that verifies that the value of a column exists
in a second table, and make it nullable.

Martijn Tonies
InterBase Workbench - the developer tool for InterBase and Firebird
http://www.interbaseworkbench.com

Upscene Productions
http://www.upscene.com

"This is an object-oriented system.
If we change anything, the users object."




I learnt how to set a constraint that verifies that the value of a column
exists in a second table.

Also I learnt how to check the values of a column against a predifined list
of values.

However, now I have to verify that a column is NULL (or empty) or contains
a value that exists in a second table.

How do I do that ?

Thank you

Duilio Foschi


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