SuiteScript 2.0 Search appears non-deterministic

I am trying to query for vendor payments using the following SuiteScript 2.0 search. The problem I am having is that the number of records the search returns seems to depend on the columns I specify. I come from a SQL background and am not used to this. If anyone can please provide some insight into this behavior, I would be greatly appreciative.

Thanks in advace,

require(['N/search', 'N/record'], function (search, record) {
    var paymentsSearch = search.create({
        type: record.Type.VENDOR_PAYMENT,
        columns: ["THE NUMBER OF RECORDS RETURNED SEEMS TO DEPEND ON THE COLUMNS IN THIS ARRAY"]
    });

    var resultSet = paymentsSearch.run();