Heuristics for Determining a Reasonable Answer Set - Teradata Database

Before you can judge the accuracy of the results returned from an outer join query, you need to estimate a reasonable guess about the likelihood that an answer set is correct. This section provides two simple methods for obtaining the approximate numbers of rows you should expect from a correctly structured outer join query.

Example 1: A single table SELECT of an outer join used for this study.

Example 2: An inner join that explains the remaining queries and results in the case study. It starts with the same base of customer rows but matches them with revenue rows for a particular month.