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Background documentation JOIN_SEARCH_LEVEL Locate the document in its SAP Library structure

The special database parameter JOIN_SEARCH_LEVEL determines the algorithm for the join sequence search. The level specified here determines how many resources and how much time the join sequence search takes.

·        9 (Join sequence search level 9): All possible join sequences are calculated (permutation algorithm).

·        4 (join sequence level 4): Various join sequences are calculated, depending on the query structure (transformer algorithm).

·        1 (join sequence search level 1): The simplest algorithm is used for the join sequence search (greedy algorithm).

·        0 (classified join sequence search level 0, level 0 is the default setting): The algorithm that is used for the join sequence search depends on the number of tables that were selected in join.

Joins with n number of tables, where n<=JOIN_MAXTAB_LEVEL9: Level 9 of the join sequence search is used.

Joins with n number of tables, where JOIN_MAXTAB_LEVEL9<n<=JOIN_MAXTAB_LEVEL4: Level 4 of the join sequence search is used.

Joins with n number of tables, where JOIN_MAXTAB_LEVEL4<n: Level 1 of the join sequence search is used.

Example

JOIN_MAXTAB_LEVEL4 is set to 16.

JOIN_MAXTAB_LEVEL9 is set to 4.

JOIN_SEARCH_LEVEL is set to 0.

5 tables are used for a join.

Join sequence search level 4 (transformer algorithm) is used for this join because JOIN_MAXTAB_LEVEL9<5<=JOIN_MAXTAB_LEVEL4 applies.

Note

For information on the way the Optimizer works, see the documentation Optimizer.

 

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