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Overview
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Sub queries permit as a 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. |
Append Queries
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The append sub query takes the results of one query and appends these to another as new columns of data. The two queries must have exactly the same GROUP BY (or Dimensional) columns in order to join them.
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See Append Sub Query Tutorial for more information.
Union Queries
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A Union query combines the results of two SQL queries into a single table of all matching rows. The two queries must have the same number of columns and compatible data types in order to join them. Any duplicate records are automatically removed unless UNION ALL is used.
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With a standard union join duplicate records are not returned so if the row in the sub query matches the row in the master query it will not be displayed, If you wish to display duplicate records you must specify this at the sub query level.
Intersect Queries
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An Intersect query takes the results of two queries and returns only rows that appear in both result sets. For example if you wanted to know which customers purchased services in Year 1 as well as Year 2 then an intersect query is needed.
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See Intersect Sub Query Tutorial for more information.
Minus Queries
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A Minus query takes the distinct rows of one query and returns the rows that do not appear in a second result set. A minus query is almost the opposite of the intersect query, rather than displaying data in common the minus subtracts data from the result set.
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See Minus Sub Query Tutorial for more information.
Advanced Sub Queries
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Advanced Sub Queries extend the basic Sub Query functionality, by allowing you to query multiple views and, in some cases, data sources.
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See Advanced Sub Query Tutorial for more information.
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