> Yes, I'm using HDR. But what means

WHERE CSNRFIRST /*>>*/ <= ? /* OLNK_CSNRFIRST */

> exactly ?

The ? will be replaced with the OLNK_CSNRFIRST parameter value.
OLNK_* parameters are ordering link parameters created and maintained
by IBO to assist with optimistation. IBO will assign this parameter
to limit records that need to be retrieved - it "refines" the
selection "horizontally" (the rows retrieved) as a means of optimising
the selection. If you have the patience you can watch the SQL monitor
to see how IBO manipulates this parameter (further explanation means
going through a great deal of code).

--
Geoff Worboys
Telesis Computing