Multidimensional analysis v16
Multidimensional analysis refers to the process of examining data using various combinations of dimensions. Dimensions are categories used to classify data such as time, geography, a company’s departments, product lines, and so forth. This process is commonly used in data warehousing applications. The results associated with a particular set of dimensions are called facts. Facts are typically figures associated with product sales, profits, volumes, counts, and so on.
To obtain these facts according to a set of dimensions in a relational database system, you typically use SQL aggregation. SQL aggregation basically means data is grouped according to certain criteria (dimensions), and the result set consists of aggregates of facts, such as counts, sums, and averages of the data in each group.
GROUP BY clause of the SQL
SELECT command supports the following extensions that simplify the process of producing aggregate results:
In addition, you can use the
GROUPING function and the
GROUPING_ID function in the
SELECT list or the
HAVING clause to aid with the interpretation of the results when you use these extensions.
emp tables are used extensively in this discussion to provide usage examples. The following changes were applied to these tables to provide more informative results:
The following rows from a join of the
dept tables are used:
job columns are used for the dimensions of the SQL aggregations used in the examples. The resulting facts of the aggregations are the number of employees obtained by using the
A basic query grouping the
job columns is given by the following:
The rows of this result set using the basic
GROUP BY clause without extensions are referred to as the base aggregate rows.
CUBE extensions add to the base aggregate rows by providing additional levels of subtotals to the result set.
GROUPING SETS extension lets you combine different types of groupings into a single result set.
GROUPING_ID functions help you to interpret the result set.
rollup_extension cube_extension grouping_sets_extension grouping_function grouping_id_function