17.05 - Evaluation Order of WHERE, GROUP BY, and QUALIFY Clauses - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQL Data Manipulation Language

Product
Advanced SQL Engine
Teradata Database
Release Number
17.05
Published
January 2021
Language
English (United States)
Last Update
2021-01-22
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When the WHERE, GROUP BY, and QUALIFY clauses are used together in a SELECT statement, the order of evaluation is as follows:
  1. WHERE clause
  2. GROUP BY clause
  3. QUALIFY clause
The detailed steps are as follows:
  1. The database evaluates the WHERE clause conditions on the FROM clause tables.
  2. The system groups the resulting rows using the GROUP BY columns.
  3. The database evaluates the ordered analytical functions on the grouped table.
  4. The system applies the QUALIFY clause to the resulting set.

Vantage-specific functions such as CSUM and MAVG that are invoked in both the select list and in the search condition of the QUALIFY clause are computed on the grouped rows without eliminating any rows and then the system applies the search condition of the QUALIFY clause.

For window functions, such as SUM and AVG, the GROUP BY collapses all rows with the same value for the group-by columns into a single row.