| 摘要 |
A method and system for efficiently joining database tables using compact row mapping structures is provided. In a preferred embodiment, a one-table row mapping structure is used to join two source tables while enforcing a restriction against a column of one of the source tables. Where the restricted column value satisfies the restriction, an indication is stored in the one-table mapping structure that the source table rows listed in that row of the index satisfy the restriction. When the source tables are joined by merging indices on the join columns of the two tables, only rows of the restricted source table for which an indication is stored in the one-table row mapping structure that it satisfies the restriction are merged. In a further embodiment, an arbitrary number of source tables are joined using a series of two-table row mapping structures, each constructed to represent the joining of two adjacent tables by mapping from rows of one of the adjacent table to rows of the other adjacent table. Each two-table row mapping structure is constructed by merging indices on the join columns of the two adjacent tables. When a row of the join result table is retrieved, a row of one of the source tables is selected, and all of the two-table mapping structures are used to identify a row of each of the other source tables to which the selected row is joined.
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