Value Set in Oracle Apps using Union


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I need to create a value set which selects items from a custom table for certain run no and union it with Select 'ALL' from dual so that when the user selects ALL the program runs for all the items. I tried creating a view of the custom table and then used oracle apps dba

select item from xx_cust_view where run_no=:$FLEX$.RUN_NO_VS union select 'ALL' from dual
It is saved without error in value set but gives an error when I try to pass values while running the program.