A select request is one or more Teradata SQL SELECT statements that may be optionally preceded by a LOCKING modifier. The following information might apply for a FastExport job, depending on how select requests were created in that job.
IMPORT Commands
If an IMPORT command is used, FastExport executes the select request once for each select data record, as specified by the FIELD commands. In this case, the response data for each execution of the select request is concatenated into the output data set.
If an IMPORT command defines input variables for the WHERE condition, the external names cited in the WHERE condition must correspond to the names in the FIELD commands.
Multiple SELECT Statements
If select request has multiple SELECT statements, Teradata Database may execute them in parallel, but still returns the response data for the first statement first, then the response data for the second, and so on.
When you specify an OUTMOD routine to process the output records, Teradata Database returns the FastExport job statement number with the response data for each SELECT statement. Otherwise, there is nothing returned to the output data set to delimit the records for one statement from those of the next.
LOCKING Modifiers
If a LOCKING modifier is used, the specified lock remains in effect during execution of all statements within the request containing the modifier.
Teradata Database does the following:
- Implements all resource locks for the entire request before executing any of the statements in the request
- Maintains the locks until all of the response data for the request has been moved to spool tables Teradata Database removes the resource locks before returning the data to the client system.
Select Statement and Table Operator
Starting from TTU 14.10, Table operators can be used in the FROM clause of SELECT statements. Table operators accept a table or table expression as input and generate a table as output. They are a type of user-defined function (UDF). For more information about Table Operators, please refer to SQL Functions, Operators, Expressions, and Predicates (B035-1145).
Select Request Restrictions
FastExport select requests cannot:
- Specify a USING modifier
To submit data parameters as restraint parameters with a SELECT statement, the must be defined using a FastExport IMPORT command with supporting FIELD and FILLER commands.
- Access nondata tables, such as SELECT DATE or SELECT USER
Other than these restrictions, Teradata Database parses and processes SELECT statements from FastExport as it would from any other data access facility.