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  1. #1
    Silver Lounger
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    SQL -- UNKNOWN (Transact-SQL)

    Several SQL references that I have seen, MSDN for example, define a predicate as "an expression that evaluates to TRUE, FALSE, or UNKNOWN." What is UNKNOWN? How do you get it? How does it differ from NULL? How do you check for UNKNOWN? Can you give me an example of an SQL SELECT statement that involves UNKNOWN? TIA --Sam
    <font face="Comic Sans MS">Sam Barrett, CACI </font face=comic>
    <small>And the things that you have heard... commit these to faithful men who will be able to teach others also. 2 Timothy 2:2</small>

  2. #2
    Plutonium Lounger
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    Re: SQL -- UNKNOWN (Transact-SQL)

    I don't think they're talking about an actual returned value, Sam. Given the full definition posted in MSDN, I suspect that "unknown" equates to unable to evaluate one side of the expression since they're talking about Where and Having clauses in SQL statements and in Joins.
    Charlotte

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