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    <p>Sack your contractor.</p> <p>Okay, seriously, this isn't standard practice. This can be seen simply because all RDBMS that I have ever worked with implement NULL, logic for NULL, take account of NULL in foreign keys, have different behaviour for NULL in COUNT, etc, etc.</p> <p>I would actually contend that using 'Z' or any other place holder is worse. You still require code to check for 'Z'. But you also need to document that 'Z' doesn't mean 'Z', it means something else. And you have to ensure that such documentation is read. And then what happens if 'Z' ever becomes a valid piece of data? (Such as a field for an initial?)</p> <p>At a basic level, even without debating the validity of NULL vs 'Z', I would insist that the contractor conforms to standard practices that exist within your company, not his. Instituting his standard practice in an environment with an alternative standard practice will cause confusion, maintenance overheads, mis-understanding, and in the end increased costs and mistakes.</p> <hr> <h3>EDIT</h3> <p>There are cases where using an alternative to NULL is valid in my opinion. But only where doing so reduces code, rather than creating special cases which require accounting for.</p> <p>I've used that for date bound data, for example. If data is valid between a start-date and an end-date, code can be simplified by not having NULL values. Instead a NULL start-date could be replaced with '01 Jan 1900' and a NULL end-date could be replaced with '31 Dec 2079'.</p> <p>This still can change behaviour from what may be expected, and so should be used with care: </p> <ul> <li><code>WHERE end-date IS NULL</code> no longer give data that is still valid </li> <li>You just created your own millennium bug </li> <li>etc.</li> </ul> <p>This is equivalent to reforming abstractions such that all properties can always have valid values. It is markedly different from implicitly encoding specific meaning into arbitrarily chosen values.</p> <p>Still, sack the contractor.</p>
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    1. POStandard use of 'Z' instead of NULL to represent missing data?
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    1. USYi Jiang
    1. USMatBailie
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    1. POStandard use of 'Z' instead of NULL to represent missing data?
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    1. CO+1 from me; spot on: "I would actually contend that using 'Z' or any other place holder is worse. You still require code to check for 'Z'. But you also need to document that 'Z' doesn't mean 'Z', it means something else. "
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      1. USMitch Wheat
    2. COWhat we need is a special value -- not NULL, since NULL is evil -- to represent missing data. Something that's different from all other values, maybe even from itself (since, two unknowns can't be equated simply because they are unknown). Some columns obviously wouldn't make sense with this value, and so it should be forbidden. To make things easy, we'd need special operators like IS UNKNOWN or IS NOT UNKNOWN.
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      1. USMike Caron
    3. COBrilliant suggestion, Mike, but I propose we use the term "Z" instead of UNKNOWN. As is, `... FROM FOO WHERE AGE IS Z`.
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      1. USWW.
 

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