In this blog, I would like to share a new functionality released in Service Layer 9.1 H Patch 12. It is about the oData aggregation, which is an important extension to the original oData protocol.
Aggregation behavior is triggered using the query option $apply. Any aggregate expression that specifies an aggregation method MUST define an alias for the resulting aggregated value. Aggregate expressions define the alias using the as keyword, followed by a Simple Identifier. The alias will introduce a dynamic property in the aggregated result set. The introduced dynamic property is added to the type containing the original expression.
Currently, the supported aggregation methods include sum, avg, min, max, count and distinctcount.
1. sum
The standard aggregation method sum can be applied to numeric values to return the sum of the non-null values, or null if there are no non-null values.
For example, to sum the DocRate of the Orders, send a request like:
GET /b1s/v1/Orders?$apply=aggregate(DocRate with sum as TotalDocRate)
On success, the response is like:
{
"odata.metadata": "$metadata#Orders(TotalDocRate)",
"value": [
{
"odata.id": null,
"TotalDocRate": 4
}
]
}
The equivalent SQL on HANA is:
SELECT SUM(T0."DocRate") AS "TotalDocRate" FROM "ORDR" T0
2 average
The standard aggregation method average can be applied to numeric values to return the sum of the non-null values divided by the count of the non-null values, or null if there are no non-null values.
For example, to calculate the average VatSum of the Orders, send a request like:
GET /b1s/v1/Orders?$apply=aggregate(VatSum with average as AvgVatSum )
On success, the response is like:
{
"odata.metadata": "$metadata#Orders(AvgVatSum)",
"value": [
{
"odata.id": null,
"AvgVatSum": 1.7
}
]
}
The equivalent SQL on HANA is:
SELECT AVG(T0."VatSum") AS "AvgVatSum" FROM "ORDR" T0
3 max
The standard aggregation method max can be applied to values with a totally ordered domain to return the largest of the non-null values, or null if there are no non-null values. The result property will have the same type as the input property.
For example, to get the maximum DocEntry of the Orders, send a request like:
GET /b1s/v1/Orders?$apply=aggregate(DocEntry with max as MaxDocEntry)
On success, the response is like:
{
"odata.metadata": "$metadata#Orders(MaxDocEntry)",
"value": [
{
"odata.id": null,
"MaxDocEntry": 6
}
]
}
The equivalent SQL on HANA is:
SELECT MAX(T0."DocEntry") AS "MaxDocEntry" FROM "ORDR" T0
4 min
The standard aggregation method min can be applied to values with a totally ordered domain to return the smallest of the non-null values, or null if there are no non-null values. The result property will have the same type as the input property.
For example, to get the minimum DocEntry of the Orders, send a request like:
GET/b1s/v1/Orders?$apply=aggregate(DocEntry with min as MinDocEntry)
On success, the response is like:
{
"odata.metadata": "$metadata#Orders(MinDocEntry)",
"value": [
{
"odata.id": null,
"MinDocEntry": 2
}
]
}
The equivalent SQL on HANA is:
SELECT MIN(T0."DocEntry") AS "MinDocEntry" FROM "ORDR" T0
5 countdistinct
The aggregation method countdistinct counts the distinct values, omitting any null values.
For example, to count the distinct CardCode of the Orders, send a request like:
GET /b1s/v1/Orders?$apply=aggregate(CardCode with countdistinct as CountDistinctCardCode )
On success, the response is like:
{
"odata.metadata": "$metadata#Orders(CountDistinctCardCode)",
"value": [
{
"odata.id": null,
"CountDistinctCardCode": "2"
}
]
}
The equivalent SQL on HANA is:
SELECT COUNT(DISTINCT T0."CardCode") AS "CountDistinctCardCode" FROM "ORDR" T0
6 count
The value of the virtual property $count is the number of instances in the input set. It MUST always specify an alias and MUST NOT specify an aggregation method.
For example, to count the number of Orders, send a request like:
GET /b1s/v1/Orders?$apply=aggregate($count as OrdersCount)
On success, the response is like:
{
"odata.metadata": "$metadata#Orders(OrdersCount)",
"value": [
{
"odata.id": null,
"OrdersCount": 4
}
]
}
The equivalent SQL on HANA is:
SELECT COUNT(T0."DocEntry") AS "OrdersCount" FROM "ORDR" T0
The above introduction is just a simple aggregation. In the subsequent patches, Service Layer is planned to enhance the aggregation by integrating it with other query options.