SAP CDS Views: Simulating Loops with Aggregation and Window Functions

In SAP ABAP CDS Views, you cannot use traditional loops like in ABAP code (e.g., LOOP statements). This is because CDS Views are designed to work declaratively with SQL-like queries and are meant to perform set-based operations, not procedural processing like loops.

However, there are ways to achieve similar functionality (e.g., aggregating data, performing operations on multiple rows, etc.) using the ABAP CDS View expressions and SQL functions.

Alternative Ways to Implement Loop-like Logic in CDS Views:

1. Aggregation (COUNT, SUM, etc.): You can aggregate data in a CDS view, which is often used instead of a loop when you need to process data in groups.

2. Window Functions (ROW_NUMBER, RANK, etc.): If you need to generate row numbers or rank data (like processing each row), window functions can be used.

3. JOINs or Subqueries: You can often simulate looping behavior through JOINs or subqueries to retrieve and manipulate data from multiple rows.

Examples of Alternatives to Loops in CDS Views:

1. Using Aggregation (COUNT, SUM, MAX, etc.)

If you’re trying to process data across rows, using aggregation functions (like SUM, COUNT, MAX, etc.) is the most common approach in CDS Views.

For example, if you want to count how many flights are available for each carrier, you can use COUNT:

define view ZFLIGHT_COUNT as select from sflight {
    key carrid,
    count( * ) as flight_count
}
group by carrid

Explanation:

• This view counts how many flights exist for each carrier (carrid), effectively simulating a loop over the flight records for each carrier and counting them.

2. Using ROW_NUMBER() or RANK() for Row-Based Processing

If you need to generate row numbers (similar to looping over rows), you can use window functions like ROW_NUMBER() or RANK().

define view ZFLIGHT_ROWNUM as select from sflight {
    key carrid,
    key connid,
    fldate,
    price,
    row_number() over (partition by carrid order by price desc) as row_num
}

Explanation:

• The ROW_NUMBER() function assigns a unique row number to each row within a partition (grouped by carrid), ordered by price in descending order.
• This simulates a form of “looping” to process rows one by one in the result set.

3. Using Subqueries or CASE Expressions

You can perform conditional operations or apply logic across rows using subqueries or CASE expressions. For instance, calculating totals or applying conditions across different rows.

define view ZFLIGHT_TOTAL_PRICE as select from sflight {
    key carrid,
    sum( price ) as total_price
}
group by carrid

Explanation:

• This view aggregates the total price of flights per carrier, simulating the “looping” behavior across all flights for each carrier.

4. Using Window Functions for More Complex Row Operations

In cases where you need operations like running totals or comparisons between rows, you can use window functions to perform those operations across rows.

define view ZFLIGHT_RUNNING_TOTAL as select from sflight {
    key carrid,
    key connid,
    fldate,
    price,
    sum( price ) over ( partition by carrid order by fldate rows between unbounded preceding and current row ) as running_total
}

Explanation:

• The SUM() window function computes a running total of the price field for each carrier, partitioned by carrid and ordered by fldate.

Key Points

• Loops are not directly supported in CDS Views since CDS operates in a set-based declarative paradigm, unlike the procedural logic of ABAP.
• Instead, you can achieve similar results using aggregation functions, window functions, subqueries, or joins.
• Aggregation allows you to compute sums, counts, and other metrics across groups.
• Window functions like ROW_NUMBER() can give each row a unique identifier, similar to looping through rows.
• CASE expressions allow you to conditionally process data and assign values based on logic.