MP Users

Optimizer and Executor

HP NonStop SQL/MX Comparison Guide for SQL/MP Users—523735-003

5-9

Statistics

In NonStop SQL/MP, the UPDATE STATISTICS statement updates the statistics stored

in the catalog for the specified table. In NonStop SQL/MX, the UPDATE STATISTICS

statement updates the histogram statistics for a group of columns within a table.

NonStop SQL/MX provides a method for generating histograms that shows how data is

distributed for a column within a table. The purpose of generating these statistics is to

enable the optimizer to create more efficient data query execution plans.

When generating a histogram for a table, NonStop SQL/MX divides the range of

specified column values of the table into some number of intervals, distributing the

rows evenly within these intervals. It computes statistics associated with each interval

and uses the statistics to devise optimized plans.

For further information, see the UPDATE STATISTICS Statement and User Metadata

(UMD)—Histogram Tables entries in the SQL/MX Reference Manual. The SQL/MX

Query Guide contains a section on keeping statistics current and best practices to

follow with respect to statistics.