Finding "surrounding" rows of a matching field?

Database experts,

I have a table with >50.000 rows and a VARCHAR2(50) column where I want to search for a pattern (maybe right-truncated). Besides getting a matching row (if there is any), I want to get 20 rows alphabetically before and after the matching row. Same if no row matches.

Since rows are not "sorted" I wonder if there is some way to use an index on that column for that purpose. Am I overlooking something? If this is not possible, will the ConText cartridge be able to solve my problem?

Thanks in advance for any help.

Herwig

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