Hazelcast Aggregation Query
Hazelcast is a distributed in memory data grid (IMDG) that provides a powerful set of features and APIs to support aggregated queries. The following are several common aggregation queries supported by Hazelcast:
1. Count: Used to calculate the number of records that meet specific conditions. Example:
IMap<String, Person> map = hz.getMap("people");
long count = map.aggregate(Aggregators.count());
2. Sum: Used to calculate the sum of the specified fields. Example:
IMap<String, Integer> map = hz.getMap("sales");
int sum = map.aggregate(Aggregators.integerSum("amount"));
3. Average: Used to calculate the average value of a specified field. Example:
IMap<String, Double> map = hz.getMap("scores");
double average = map.aggregate(Aggregators.doubleAvg("score"));
4. Min/Max: Used to find the minimum or maximum value of the specified field. Example:
IMap<String, Integer> map = hz.getMap("grades");
int min = map.aggregate(Aggregators.integerMin("score"));
int max = map.aggregate(Aggregators.integerMax("score"));
5. Group By: Used to group and perform statistics based on specified fields. Example:
IMap<Integer, Person> map = hz.getMap("people");
Map<String, Integer> ageCount = map.aggregate(Aggregators.groupBy("age", Aggregators.count()));
6. Top N (take the top N records): used to query the top N records that meet specific conditions. Example:
IMap<String, Integer> map = hz.getMap("scores");
List<Map.Entry<String, Integer>> top5 = map.entrySet()
.stream()
.sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
.limit(5)
.collect(Collectors.toList());
In the above example, we assume the existence of the following table structure and sample data:
Table name: people
|Id | name | age|
|----|-------|-----|
|1 | Alice | 25|
|2 | Bob | 30|
|3 | Carol | 25|
Table name: sales
|ID | amount|
|----|--------|
|1 | 100|
|2 | 200|
|3 | 300|
Table name: scores
|Id | score|
|----|-------|
|1 | 80|
|2 | 90|
|3 | 95|
Table name: grades
|Id | score|
|----|-------|
|1 | 80|
|2 | 90|
|3 | 95|
Please implement an aggregation query based on the above example.