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by cmeacham98
1961 days ago
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Because the database has to decided whether or not to use the index. If it decides to use the index, and there are values above 7, then it will misbehave (the query will miss those results). Now of course the database could then scan the rows for values above 7 it missed but at that point there's no point in using the index and you might as well have row scanned for the original query. As a result, the database has to be 100% sure that there are no values _at all_ above 7 to safely and efficiently use the index, ex. when there's a constraint. |
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