Lets you preview the cost of a query, in terms of I/O, before any
    rows are actually returned. For example:

    SQL> SELECT * FROM EMPLOYEES;
    Estimate of query cost: 52 I/O s, rows to deliver: 100
    Do you wish to cancel this query (No)? YES
    %SQL-F-QUERYCAN, Query cancelled at user s request

    Some queries can result in Oracle Rdb performing a large number
    of I/O operations, retrieving a large number of rows, or both.
    The SET QUERY CONFIRM statement causes SQL to display estimated
    query costs. If the cost appears excessive, you can cancel the
    query by answering No; to continue, answer Yes.

    The SET QUERY CONFIRM statement is only available for interactive
    SQL.