Using CHAIN instead of SETLL AND READE to begin a loop which reads a groupof records.

I can't find any documentation that addresses this.

If there is a table of order detail which has an index on Order #, and UPC.
Will these two pieces of code execute identically.

1.   MYORD#    CHAIN     ORDDTL    99
     *IN99          DOWEQ*OFF
               <SOMECODE>
     MYORD#    READE     ORDDTL          99
               ENDDO

2.   MYORD#    SETLL     ORDDTL
     MYORD#    READE     ORDDTL          99
     *IN99          DOWEQ*OFF
               <SOMECODE>
     MYORD#    READE     ORDDTL          99
               ENDDO

What if the index is not unique?  What if I set my pointer past the end of
file before execution?

Human logic dictates that a CHAIN should return the first occurrence of the
index which would be the smallest upc.  Computer implementation dictates
that the CHAIN should return the first occurrence of MYORD# found via an
algorithm.

So, does the algorithm match human logic?

Ever wonder why the 1st array element in most programming languages is 0?
Or is it just me...

Regards,

Mark