GENERATE STATISTICS command

Although the IBM® Netezza® system automatically maintains certain statistics, you might want to run GENERATE STATISTICS command periodically, or in the following cases:

• When you have significantly changed the nature of your database, that is, increased or decreased the number of distinct values, expanded or reduced the min/max values on joinable or groupable fields, or increased or decreased the size of your database.
• When you have static tables that you intend to keep for a long time
• When you have queries that involve three or more joins
• When you change your tables and observe slower performance when querying the updated tables
• When you have columns that are used in WHERE, SORT, GROUP BY, or HAVING clauses
• When you have temporary tables that contain many rows and that are used in JOIN clauses