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When the relationship is 1:many (refer to access route Maximum Records), the operations are TOTAL, MAXIMUM, MINIMUM, AVERAGE, and COUNT. (Also refer to PJC Type in the Technical Reference Guide.)
When the relationship is 1:1 using the key defined on the access route, a single value LOOKUP will be retrieved into the Predetermined Join Column. For example, a product description can be retrieved using the product code if an access route has been defined between an order line table and a product table. A Keep Last value can be nominated to reduce I/Os.
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- Predetermined join columns are very efficient when used to look up descriptions in code tables where the table accessed is a high speed table but overuse of this facility could cause the opposite effect, particularly in DBOPTIMISED functions when the accessed table is not a high speed table.
- As a guide, do not access more than 10 to 15 tables for Predetermined Join Columns.
See Also
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