What does GROUP BY rollup do?
GROUP BY ROLLUP is an extension of the GROUP BY clause that produces sub-total rows (in addition to the grouped rows). Sub-total rows are rows that further aggregate whose values are derived by computing the same aggregate functions that were used to produce the grouped rows.
What does rollup mean in SQL?
ROLLUP enables a SELECT statement to calculate multiple levels of subtotals across a specified group of dimensions. It also calculates a grand total. ROLLUP is a simple extension to the GROUP BY clause, so its syntax is extremely easy to use. The ROLLUP extension is highly efficient, adding minimal overhead to a query.
How many grouping is possible in the rollup?
Finally, it creates a grand total. ROLLUP creates subtotals at n+1 levels, where n is the number of grouping columns. For instance, if a query specifies ROLLUP on grouping columns of time , region , and department(n=3) , the result set will include rows at four aggregation levels.
What is GROUP BY in SQL Server?
The GROUP BY clause in SQL Server allows grouping of rows of a query. Generally, GROUP BY is used with an aggregate SQL Server function, such as SUM, AVG, etc. In addition, the GROUP BY can also be used with optional components such as Cube, Rollup and Grouping Sets.
What is coalesce in Snowflake?
Returns the first non-NULL expression among its arguments, or NULL if all its arguments are NULL.
How does grouping sets work?
GROUP BY GROUPING SETS is equivalent to the UNION of two or more GROUP BY operations in the same result set: GROUP BY GROUPING SETS((a)) is equivalent to the single grouping set operation GROUP BY a . GROUP BY GROUPING SETS((a),(b)) is equivalent to GROUP BY a UNION ALL GROUP BY b .
How do I get subtotals in SQL?
In order to calculate a subtotal in SQL query, we can use the ROLLUP extension of the GROUP BY statement. The ROLLUP extension allows us to generate hierarchical subtotal rows according to its input columns and it also adds a grand total row to the result set.
What rollup means?
transitive verb. : to increase or acquire by successive accumulations : accumulate rolled up a large majority. intransitive verb. 1 : to become larger by successive accumulations. 2 : to arrive in a vehicle.
Is distinct a grouping function?
Distinct is used to find unique/distinct records where as a group by is used to group a selected set of rows into summary rows by one or more columns or an expression. The functional difference is thus obvious.
What is OLAP used for?
OLAP (for online analytical processing) is software for performing multidimensional analysis at high speeds on large volumes of data from a data warehouse, data mart, or some other unified, centralized data store.