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Sub queries permit as user to generate far more sophisticated reports. For example if you wanted to compare the sales results of this financial year with past years you may wish to use an append query or if you wanted to determine which customers were new in a particular year you would use a minus query. In both these examples Yellowfin is generating two distinct queries and then combining the result set to provide you with a single table of results. With Yellowfin you can create 4 types of sub query, these are:
| Append | The append sub query takes the results of one query and appends them to another set of results as additional columns. The purpose of this query is to allow the result of one query to be compared to that of another. |
| Union | The union sub query combines the results of two queries into a single table of matching columns. Unions can be useful in a data warehouse application when tables aren't perfectly normalised. |
| Minus | The minus sub query takes distinct rows of one query and returns the rows that don't appear in the second query. |
| Intersect | The intersect query takes the results of two queries and returns only the rows that appear in both sets. |
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