| 摘要 |
Key conditioning involves the construction of a byte orderable array from values for a possibly multi-field key concatenated key, for comparison by a sort routine. Byte-orderable sort keys are conditioned prior to execution of a sort routine, to facilitate an accurate and/or efficient sort procedure. For example, key conditioning may be applied to values in one or more columns of a database table, where the column(s) are used as keys for sorting rows of the table. Six factors are considered in encoding the byte array, such as whether nulls compare high or low; whether a field is fixed width or variable width; whether a field is guaranteed to be not null; whether a field is ordered ascending or descending; whether a field is the last field of a multi-field sort key or the only field of a sort key; and whether a field is likely to contain a significant number of zero values.
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