APEX Collections and Joins

APEX Collections is one of the best features of APEX. There are situations where solutions wouldn't be possible if this feature would not be available. However, the collections have some limitations. One of the limitations is if you need to store number values and use those values to join a collection with other tables. The consequences may be that you receive something like

ORA-01722: invalid number

The strange thing with this error is that it may occur sporadic and you can't realy understand why it happens. If you operate on different systems (development, testing, production) you may receive this error on one of the instances and never on the other one. I asked Patrick Wolf about the reasons and he answered that this has to do with the way the cost based optimizer works. If it uses a different plan from the one you would expect, it may find non numeric values in the same column comming from a different collection. In that case the solution is to use the numeric columns in the collection (n0xx) for storing numeric values used in later joins.