Collects various table demographic estimates and writes the data to the DataDemographics table of a user-defined QCD database for subsequent analysis by the Teradata Index Wizard.
COLLECT DEMOGRAPHICS is a Teradata extension to the ANSI SQL:2011 standard.
- DELETE on the DataDemographics table in QCD_name.
- INSERT on the DataDemographics table in QCD_name or INSERT on the QCD_name database.
- SELECT on the specified tables or containing databases or users.
Normally invoked using the Teradata Index Wizard utility or the Visual Explain tool.
- Subtable type
- Subtable ID
- Estimated cardinality
- Estimated average row length
- Various system-related information
One row of information is collected in the appropriate DataDemographics subtable of the specified QCD for each AMP that is online at the time the request is performed.
COLLECT DEMOGRAPHICS does not capture information for the QCD table TableStatistics. TableStatistics is used only during the collection of statistics invoked by performing an INSERT EXPLAIN … WITH STATISTICS or COLLECT STATISTICS (QCD Form) request.
For more detailed information, see Teradata Vantage™ - SQL Request and Transaction Processing, B035-1142.
Relationship to INSERT EXPLAIN WITH STATISTICS AND DEMOGRAPHICS
- INSERT EXPLAIN WITH STATISTICS AND DEMOGRAPHICS uses an SQL query to collect the information, while COLLECT DEMOGRAPHICS obtains the information directly.
- Demographics captured by INSERT EXPLAIN WITH STATISTICS AND DEMOGRAPHICS are automatically deleted whenever you delete the relevant query plans.
Demographics captured by COLLECT DEMOGRAPHICS are not deleted when you perform associated DROP actions on the subject table and must be deleted explicitly.
COLLECT DEMOGRAPHICS Not Supported From Macros
You cannot specify a COLLECT DEMOGRAPHICS request from a macro. If you execute a macro that contains a COLLECT DEMOGRAPHICS request, the database aborts the request and returns an error.