>>OK let's say parent-child connecting key (relation) is FKfield build with expression 'index on FKField tag FKField' and here you :
>>set filter to ADCPStreet
>>for extra filtering. Instead an index (created on the fly then deleted or once created persists) :
>>index on FKField+transform(ADCPStreet) tag mySpecial
>>or :
>>index on FKField tag mySpecial for ADCPStreet
>>would do the job.
>>In first you would set your RelationalExpr to ParentPK+'T'.
>>Cetin
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>Sorry, Cetin, I'm not sure, I understood. This application has only one table - WorkFile, all other tables are used to perform some operations (I don't have any relations). So, do you suggest a filtered index? Would it be the same, as set filter?

No not the same, better:)
Cetin