Talk:Check constraint

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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)[reply]

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)[reply]