SQL Sampling
A database is often used for transactional purposes, but one of the major benefits of the relational model is the ability to perform complex analysis of the data. DB2 has many features and techniques that improve the performance of complex queries including summary tables, dynamic bitmap indexes, MDC, and a variety of SQL optimizations.
DB2 UDB v8.1 introduces another type of SQL optimization in the form of sampling of data during the execution of a statement. Databases are growing so large that it is often impractical to access all of the data relevant to a query. For instance, a query requesting the average sales per month in a large department store might need to read millions of records. In this example, it might be just as valid ...
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