oracle - Enforcement of unique/primary key - drop index -

i trying drop index :

drop index pk_charges 

but error

cannot drop index used enforcement of unique/primary key

why getting error? provide further information if need any.

how solve it?

edit have no primary key in table, found weird index don't remember had added:

index name = sys_c0040476 have same columns

you can query all_constraints performance view see constraint index used by, , table applies to, e.g:

select owner, constraint_name, constraint_type,     table_name, index_owner, index_name all_constraints index_name = 'pk_charges'; 

i expect table name 'charges', constraint name match index name, , constraint type 'p'. since have table in mind, perhaps names aren't following helpful convention. maybe old version of table renamed, leave constraints against new name (e.g. charges_backup or something).

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you said click on table, on view. perhaps you're not looking @ table constraint/index on; or perhaps you're looking @ view on top of actual table. mention sys_ index on same columns - can't on same table. have multiple similar tables, or access multiple schemas? shold run above query index too. mentions above, might find old version (or versions) of table.

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once you've identified table constraint on, you'll need decide whether should keeping it, , if not can remove dropping constraint alter table command.