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
In database management, an aggregate function or aggregation function is a function where the values of multiple rows are grouped together to form a single summary value.
Common aggregate functions include:
* Average (i.e., arithmetic mean)
* ...
for each group.
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.
Examples
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
Returns the data of the example
pivot table
A pivot table is a table of grouped values that aggregates the individual items of a more extensive table (such as from a database, spreadsheet, or business intelligence program) within one or more discrete categories. This summary might include ...
which answers the question "How many Units did we sell 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 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
*
Aggregate function
In database management, an aggregate function or aggregation function is a function where the values of multiple rows are grouped together to form a single summary value.
Common aggregate functions include:
* Average (i.e., arithmetic mean)
* ...
References
External links
SQL Snippets: SQL Features Tutorials - Grouping Rows with GROUP BY
SQL keywords
Articles with example SQL code
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