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> 有没有这句话的出处
Diagnosing Why a Query is Not Using an Index [ID 67522.1]
Are the indexed columns NULLable?
Indexes do NOT store NULL values unless the index is concatenated (i.e. multi-column indexes), or it is a Bitmap index. For concatenated indexes NULLs are only stored if at least one of the indexed columns is filled. ... Rows are not stored if all the indexed columns are NULL. |
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楼主: sxitsxit
IP卡
狗仔卡
发表于 2013-4-10 00:37
显身卡
楼主
发表于 2013-8-30 16:10