| 摘要 |
A query formulates choices of multiple equivalent forms. A choice is represented by a CHOOSE operator having multiple arguments representing the equivalent forms. A lookup table is generated to include a group for each node other than CHOOSE arguments. For CHOOSE arguments, the generated table includes a single equivalence group having all choose arguments as members. The enumeration algorithm of the optimizer is applied to generate additional members and/or groups, whereby for each group, every member thereof is an equivalent. A cost value is assigned to each member of each group and a member of each group is selected as a lowest cost value member. The lowest cost value members of the groups define an optimized tree and optimization of the query.
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