Performance Considerations - Teradata Database

Performance Considerations

For best performance, use the TOP N option instead of the QUALIFY clause with RANK or ROW_NUMBER.

In best cases, the TOP N option provides better performance.

In worse cases, the TOP N option provides equivalent performance.

See “SELECT” on page 8.

If a SELECT statement using the TOP N option does not also specify an ORDER BY clause, the performance of the SELECT statement is better with BTEQ than with FastExport.

A recursive query is a way to query hierarchies of data, such as an organizational structure, bill-of-materials, and document hierarchy.

Recursion is typically characterized by three steps:

Initialization

Recursion, or repeated iteration of the logic through the hierarchy

Termination

Similarly, a recursive query has three execution phases:

Initial result set

Iteration based on the existing result set

Final query to return the final result set