A method and apparatus disclosed may be implemented in a digital computer to query a set of arbitrarily structured records. Arbitrarily structured records are structured differently from each other. A query engine, query structure, operators of conventional and non-conventional types may be used in formulating a query. The apparatus may evaluate records having missing fields, repeating fields, or an UNKNOWN value arising from a missing field, division by zero, modulo by zero, or the like. New aggregator (e.g. universal quantifier and existential quantifier) and selector operators (e.g., first, last, nth) may distill multiple values to return a single value. To evaluate a query, the search engine may implement filtered indices, alternate-key indices, compound alternate-key indices, hybrid queries having both full-text and non-full text operands, and joinder of records. Certain of these features may be implemented for evaluating records from both prior art databases and heterogeneous databases of arbitrarily structured records.