Oracle Message ORA-04091 - table string.string is mutating, trigger/function may not see it

ERRORtable string.string is mutating, trigger/function may not see it
CAUSEA trigger (or a user defined plsql function that is referenced in this statement) attempted to look at (or modify) a table that was in the middle of being modified by the statement which fired it.
ACTIONRewrite the trigger (or function) so it does not read that table.