HP 3000 Manuals HP 3000 Manuals
IMSAM Composite Keys IMSAM supports a feature called composite keys, which are constructed from parts of one or more data items in a dataset. For example, suppose DATABASE1 has data items ACCTNUM and DEPTNUM, each three bytes long, and DATABASE2 has a data item ACCTDEPT that holds the ACCT number and DEPT number merged into one field. This appendix shows you how a view table with SUB and concatenation functions would let you JOIN data from these two databases. The same result could be achieved with IMSAM composite keys. DATABASE2, which has the 6-character field ACCTDEPT, could make composite keys for the first three bytes and second three bytes of ACCTDEPT. These keys could be used for fast keyed JOINs of tables from DATABASE1 and DATABASE2. Alternatively, DATABASE1 could make one composite key built from ACCTNUM and DEPTNUM, and use this for fast keyed JOINs with the ACCTDEPT field in DATABASE2.