| --- |
| title: OQL Aggregate Functions |
| --- |
| |
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| |
| The aggregate functions |
| ```MIN```, |
| ```MAX```, |
| ```AVG```, |
| ```AVG``` over a DISTINCT expression, |
| ```SUM```, |
| ```SUM``` over a DISTINCT expression, |
| ```COUNT```, and |
| ```COUNT``` over a DISTINCT expression |
| are supported. |
| The ```GROUP BY``` extension is also supported, and required whenever an aggregate function is used within a query with other selected fields. |
| If there are no other aggregate functions within the query, then all fields included within a ```GROUP BY``` clause must also be part of the original projection list, and all fields included within the projection list must also be part of the ```GROUP BY``` clause. |
| |
| The ```MIN``` function returns the smallest of the selected |
| expression. |
| The type of the expression must evaluate to a |
| ```java.lang.Comparable```. |
| |
| The ```MAX``` function returns the largest of the selected |
| expression. |
| The type of the expression must evaluate to a |
| ```java.lang.Comparable```. |
| |
| The ```AVG``` function returns the arithmetic mean of the set |
| formed by the selected expression. |
| The type of the expression must evaluate to a |
| ```java.lang.Number```. |
| For partitioned regions, |
| each node's buckets provide both a sum and the number of elements |
| to the node executing the query, |
| such that a correct average may be computed. |
| |
| The ```AVG``` function where the DISTINCT modifier is applied |
| to the expression returns the arithmetic mean of the set |
| of unique (distinct) values. |
| The type of the expression must evaluate to a |
| ```java.lang.Number```. |
| For partitioned regions, |
| the distinct values in a node's buckets are returned |
| to the node executing the query. |
| The query node can then calculate the avarage over |
| the values that are unique across nodes, |
| after eliminating duplicate values that come from separate nodes. |
| |
| The ```SUM``` function returns the sum over the set |
| formed by the selected expression. |
| The type of the expression must evaluate to a |
| ```java.lang.Number```. |
| For partitioned regions, |
| each node's buckets compute a sum over that node, |
| returning that sum |
| to the node executing the query, |
| when then sums across all nodes. |
| |
| The ```SUM``` function where the DISTINCT modifier is applied |
| to the expression returns the sum over the set |
| of unique (distinct) values. |
| The type of the expression must evaluate to a |
| ```java.lang.Number```. |
| For partitioned regions, |
| the distinct values in a node's buckets are returned |
| to the node executing the query. |
| The query node can then calculate the sum over |
| the values that are unique across nodes, |
| after eliminating duplicate values that come from separate nodes. |
| |
| The ```COUNT``` function returns the quantity of values in the set |
| formed by the selected expression. |
| For example, to return the quantity of employees who have a |
| positive sales amount: |
| |
| ``` pre |
| SELECT count(e.sales) FROM /employees e WHERE e.sales > 0.0 |
| ``` |
| |
| The ```COUNT``` function where the DISTINCT modifier is applied |
| returns the quantity of unique (distinct) values in the set |
| formed by the selected expression. |
| |
| ## GROUP BY Extension for Aggregate Functions |
| |
| ```GROUP BY``` is required |
| when aggregate functions are used in combination |
| with other selected items. |
| It permits ordering. |
| For example, |
| |
| ``` pre |
| SELECT ID, MAX(e.sales) FROM /employees e GROUP BY ID |
| ``` |