main_index - MAIN_ORDER option
Usually, the first index, which is not temporary and not unique is considered as main index. Since this depends on the key name, it is more save to mark the main index index explicitly as such.
Only one index should be marked as main order. Further settings are ignored.
Notes:
Main index settings are not checked. When marking more than one index as main index, this will not cause an error, i.e. it might cause unexpected results.
Type: logical