Query engine overview

IBM® DB2® for i provides two query engines to process queries: Classic Query Engine (CQE) and SQL Query Engine (SQE).

SQL-based interfaces, such as ODBC, JDBC, CLI, Query Manager, Net.Data®, RUNSQLSTM, and embedded or interactive SQL, run through SQE. Also by default some non-SQL based interface such as OPNQRYF and Query/400 will run through SQE. The CQE processes queries originating from non-SQL interfaces: QQQQry API. For ease of use, the routing decision for processing the query by either CQE or SQE is pervasive and under the control of the system. The requesting user or application program cannot control or influence this behavior except for non-SQL interfaces through use of a QAQQINI. However, a better understanding of the engines and process that determines which path a query takes can give you a better understanding of query performance.

Within SQE, several more components were created and other existing components were updated. Additionally, new data access methods are possible with SQE that are not supported under CQE.