When to Use the SQL Statistics Statements

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Mimer SQL collects basic statistics for each table whenever the table is opened. These statistics may suffice for maintaining high performance in many situations.

If optimal performance is required for an application, the SQL statistics statements should be used to collect detailed information (this includes information on value distribution and table size).

When this is the case, statistics should be typically updated in the following situations:

• when the size of a table has changed significantly
• when the maximum/minimum limits on values in a table have altered significantly
• when a databank has been altered from having the WORK option to having the TRANSACTION or LOG option and contains secondary indexes
• when a databank with the TRANSACTION or LOG option contains secondary indexes and has just been upgraded from Mimer SQL version 7 or 8.1.

The statistics information in the data dictionary is used only by the Mimer SQL compiler.

Note: Only the performance, not the result, of an SQL statement is affected by gathering and using the statistical information and by ensuring the consistency of secondary indexes.

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