DB2中高效SQL语句的最佳实践 oin Method),常见的连接方法有嵌套循环连接(Nested-Loop-Join, NLJ),归并排序连接(Merge-Scan-Join, MSJoin),哈希连接(Hash-Join)等。DB2 优化器会根据实际情况选择从中选取一个性能最佳的来将 T1
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DB2中高效SQL语句的最佳实践 oin Method),常见的连接方法有嵌套循环连接(Nested-Loop-Join, NLJ),归并排序连接(Merge-Scan-Join, MSJoin),哈希连接(Hash-Join)等。DB2 优化器会根据实际情况选择从中选取一个性能最佳的来将 T1
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Typically, the optimizer chooses merge scan join when the cardinality of the outer input is not obviously small and there is no efficient access method for the inner table.
通常情况下,在外部输入的基数显然不小且对于内部表没有一种有效的访问方法时,优化器会选择合并扫描联接。
As previously stated, ordered input is essential to a merge scan join, but it is not required for nested loop joins.
如前所述,按顺序的输入对于合并扫描联接是必不可少的,但其无需嵌套循环联接。
For the merge scan join to perform properly, both inputs are expected to be in the order of join columns.
为了合并扫描联接正确地执行,按照联接列的顺序预计有两个输入。
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