Optimizing SQL Queries

August 1997 / Reviews / IBM Builds a Better DBMS / Optimizing SQL Queries

DB2 subjects SQL statements to one of nine levels of optimization just prior to processing those statements. The nine levels, configurable by a database administrator or settable by applications software, allow precise tuning of database response times. For example, you'd use level 0 or 1 for SQL that's already optimized by the pro grammer. Higher levels let DB2 examine and reformat SQL that's been submitted by, for instance, a front-end query tool such as Microsoft Access or Lotus Approach 97.
The SQL optimizer uses cost-based algorithms to determine the most effici ent execution method. The optimizer finds the best join order, for example, and it decides whether the execution of the SQL statement will be CPU- or I/O-bound. The optimizer chooses an execution path for the SQL statement that will result in the quickest response from the database engine.

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Matthew Wilson
My approach to software engineering is far more pragmatic than it is theoretical--and no language better exemplifies this than C++.

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