# Index Selection Considerations (Continue...)


![left](./student-guide/diagram/19-Index-selected-dimensions-02-01.png)

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For example, we created three indexes, a single-column index on column b and column e, and a composite index on columns b and c. For the above three dimensions, if the index idx_a is not worse than idx_b in all three dimensions, and there is one dimension better than idx_b, then TiDB will give preference to idx_a. Execute EXPLAIN FORMAT = 'verbose'... statement, if some indexes are excluded by Skyline-Pruning, TiDB will output a NOTE level warning indicating which indexes are retained after Skyline-Pruning exclusions.

In the following example, the indexes idx_b and idx_e are both inferior to idx_b_c and are therefore excluded from Skyline-Pruning. The result of SHOW WARNING shows the indexes remaining after Skyline-Pruning.