Find matching value across two different question groups
S.VISIT_NUMBER = 36
S.DCM_DATE =
S.REPEAT_SN = 1
S.SAENO = 02 (Retrieves this value. Now to look for matching value.)
A.VISIT_NUMBER = 30
A.DCM_DATE =
A.REPEAT_SN = 1
A.AENO = 01 (Evaluate but don't execute. No match yet.)
A.VISIT_NUMBER = 30
A.DCM_DATE =
A.REPEAT_SN = 1
A.AENO = 02 (Evaluate but don't execute. Got a match!)