>>>The column DATEI is defined as C(240) and has an index on UPPER(DATEI).
>
>To use the index, you need the filter to be UPPER(datei) as well.
>
>

WHERE UPPER(Datei) = UPPER(lcPfad)

>
>With no index on Datei, a filter on Datei does a table scan.

That will force Rushmore to kick in, but still runs some unneccessary UPPER() calls following the btree.

local lcUpperPfad
lcUpperPfad =  UPPER(lcPfad)
SELECT Datei FROM ("DBCNAME!" + lcTabelle) ;
		WHERE UPPER(Datei) =  m.lcUpperPfad;
		INTO CURSOR TMP_DOKNAME

is somewhere between having good habits and premature optimization ;-))