A GROUP BY
statement in SQL specifies that a SQL SELECT
statement partitions result rows into groups, based on their values in one or several columns. Typically, grouping is used to apply some sort of aggregate function for each group.[1][2]
The result of a query using a GROUP BY
statement contains one row for each group. This implies constraints on the columns that can appear in the associated SELECT
clause. As a general rule, the SELECT
clause may only contain columns with a unique value per group. This includes columns that appear in the GROUP BY
clause as well as aggregates resulting in one value per group.[3]
Examples
[edit]Returns a list of Department IDs along with the sum of their sales for the date of January 1, 2000.
SELECT DeptID, SUM(SaleAmount) FROM Sales
WHERE SaleDate = '01-Jan-2000'
GROUP BY DeptID
In the following example one can ask "How many units were sold in each region for every ship date?":
Sum of units | Ship date ▼ | |||||
---|---|---|---|---|---|---|
Region ▼ | 2005-01-31 | 2005-02-28 | 2005-03-31 | 2005-04-30 | 2005-05-31 | 2005-06-30 |
East | 66 | 80 | 102 | 116 | 127 | 125 |
North | 96 | 117 | 138 | 151 | 154 | 156 |
South | 123 | 141 | 157 | 178 | 191 | 202 |
West | 78 | 97 | 117 | 136 | 150 | 157 |
(blank) | ||||||
Grand total | 363 | 435 | 514 | 581 | 622 | 640 |
The following code returns the data of the above pivot table which answers the question "How many units were sold in each region for every ship date?":
SELECT Region, Ship_Date, SUM(Units) AS Sum_of_Units
FROM FlatData
GROUP BY Region, Ship_Date
Common groupings
[edit]Common grouping (aggregation) functions include:
- Count(expression) - Quantity of matching records (per group)
- Sum(expression) - Summation of given value (per group)
- Min(expression) - Minimum of given value (per group)
- Max(expression) - Maximum of given value (per group)
- Avg(expression) - Average of given value (per group)
See also
[edit]References
[edit]- ^ "SQL GROUP BY Statement". www.w3schools.com. Retrieved 2020-09-18.
- ^ shkale-msft. "GROUP BY (Transact-SQL) - SQL Server". docs.microsoft.com. Retrieved 2020-09-18.
- ^ "SQL Grouping and Aggregation". databaselecture.com. Retrieved 2020-12-09.
External links
[edit]
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction