Talk:Check constraint

Remark

Added links to this page from:

http://en.wikipedia.org/wiki/Update_%28SQL%29

http://en.wikipedia.org/wiki/Insert_%28SQL%29

http://en.wikipedia.org/wiki/SQL-92

http://en.wikipedia.org/wiki/Virtuoso_Universal_Server

This article currently has the following examples

Some examples of dangerous constraints include:

CHECK ((select count(*) from invoices where invoices.customerId = customerId) < 1000)

CHECK (dateInserted = CURRENT_DATE)

CHECK (countItems = RAND())

What is "dangerous" with these check constraints? --Abdull (talk) 15:34, 26 September 2012 (UTC)

UNKNOWN?

Why does this article refer to UNKNOWN? In SQL 'unknown' is represented by NULL, so surely this should say NULL? 80.41.77.9 (talk) 11:13, 16 August 2021 (UTC)