GemStone/S Aggregate Query
GemStone/S is a Object database management system that supports multiple aggregate query operations. The following are some common aggregation query examples supported by GemStone/S and their implementation methods:
1. COUNT query: used to calculate the number of objects that meet specific conditions.
Table structure example:
class Order {
id: Integer;
totalAmount: Double;
customerId: Integer;
}
Example query: Calculate the quantity of all orders.
smalltalk
|Count|
count := Order count.
2. SUM query: Calculate the total of a certain field.
Example query: Calculate the total amount of all orders.
smalltalk
|TotalAmount|
totalAmount := Order sum: #totalAmount.
3. AVG query: Calculate the average value of a certain field.
Example query: Calculate the average amount of all orders.
smalltalk
|AverageAmount|
averageAmount := (Order sum: #totalAmount) / (Order count).
4. MAX query and MIN query: calculate the maximum and minimum values of a certain field separately.
Example query: Calculate the maximum and minimum amounts for all orders.
smalltalk
|MaxAmount minAmount|
maxAmount := Order max: #totalAmount.
minAmount := Order min: #totalAmount.
5. GROUP BY query: Group by the value of a certain field and perform aggregation operations on each group.
Example query: Calculate the order quantity for each customer by grouping them by customer ID.
smalltalk
Order aggregateWith: {: each | each customerId}
Collect: # count in: [: counts | counts asDictionary]
6. HAVING query: Based on the GROUP BY query, further filter groups that meet specific conditions.
Example query: Calculate the number of customers with a total order amount exceeding 100.
smalltalk
|CustomerCount|
CustomerCount:=(Order aggregateWith: {: each | each customerId}
Collect: # sum: totalAmount in: [: total | total asDictionary])
Count: [: each | each value>100]
These examples demonstrate some common aggregation query operations supported by GemStone/S. Please note that GemStone/S is an object-oriented database system, so the query syntax is using the Smalltalk programming language. The table structure example is for reference only and needs to be adjusted according to specific needs during actual use.
