1. Define SAP HANA, and how is it different from a traditional database?

SAP HANA is a column-based, in-memory RDBMS. HANA is column-based iterative rather than the traditional row-based iterative databases (like Oracle or SQL Server). HANA is faster than traditional DBs for aggregations and analytic queries. All the data for ABAP developers is stored in RAM, so traditional DB I/O disk bottlenecks are removed. The good part for ABAP developers is the performance bottleneck comes from the database, meaning the focus should be on the application layer, and complex ABAP should be pushed to the database.

2. Explain the "Code Pushdown" principle in SAP ABAP on HANA?

Code Pushdown (or "data-to-code" vs "code-to-data") is a fundamental principle of ABAP on HANA. The first processing bottleneck for ABAP on HANA is the application server. Instead of bringing a large dataset to the application server and processing it using ABAP logic (loops, aggregations, sorts), the bottleneck should be pushed to the HANA Database Server. When using the HANA Database Server, processing is far faster, as it is all done in-memory. This is especially the case when using a large dataset.

• CDS Views (Core Data Services)
• AMDP (ABAP Managed Database Procedures)
• Open SQL with aggregations and JOINs
• Native SQL via ADBC

3. What are Core Data Services (CDS) in SAP ABAP?

CDS enables the definition of semantically rich data model projections. Building of CDS views is done in the database and done in the context of data model semantic definition. CDS views are then used in ABAP outlining (re-engineering) programs, OData inquiries and analysis tools.

The main capabilities of CDS views are as follows:

• The JOIN, aggregation, and CASE functionalities and built-in functions are all available.
• They contain annotations, which can be box-strapped for Fiori, vertical analysis, and security.
• As data sources in SELECT commands, they can be employed.
• These views are association-based navigable.

4. What is an AMDP (ABAP Managed Database Procedure)?

AMDP is a framework for ABAP developers that makes it possible to implement database procedures (SQLScript for HANA) in ABAP classes. SQLScript runs directly on the HANA database engine, and thus is suitable for analytical logic that is memory intensive.

An AMDP class:

• Implements the interface IF_AMDP_MARKER_HDB
• Methods use the addition BY DATABASE PROCEDURE FOR HDB LANGUAGE SQLSCRIPT
• Input and output parameters are declared as ABAP types

5. What is the difference between Open SQL and Native SQL in SAP ABAP?

Open SQL is preferred for portability and maintainability. Native SQL via AMDP is preferred for maximum HANA performance in complex scenarios.

6. What is the Eclipse-based ADT (ABAP Development Tools)?

ADT is the modern development environment for SAP ABAP, built as a plugin for Eclipse IDE. It replaces the traditional SAP GUI-based SE38/SE80 for many development tasks and is mandatory for developing CDS views and AMDP. Key capabilities include:

• Creating and editing CDS views, AMDP, and Business Object types
• Syntax checking and code completion
• Integrated performance analysis with HANA tools
• Git-based version control integration (abapGit)

7. How many kinds of CDS views exist when it comes to Development of SAP ABAP on HANA?

There are at least five main categories of CDS views:

• Basic CDS Views – are simple views that can read data either directly from database tables or from another CDS view.
• Composite CDS Views – are views layered on top of other CDS views with some additional logic or filtering.
• Consumption CDS Views – can usually be consumed directly by applications (e.g., Fiori apps and OData) and are usually annotated with UI metadata.
• Interface CDS Views – serves as a stable interface for external consumers and acts as an abstraction from the underlying data model.
• VDM CDS Views – are a part of the pre-provided CDS content by SAP S/4HANA that are designed for analytics and reporting.

8. How would you describe both the purpose and syllabi of annotations in a CDS View? Please give at least three examples.

Annotations are additional content to CDS views that indicate to the authors of the view information about the view. They indicate the class (data) and control view behavior in the different environments where the views are hosted. Examples are the following:

• @AbapCatalog.sqlViewName — Appends a name to a basic SQL view within the ABAP dictionary.
• @Analytics.dataCategory: #CUBE — Designates the view for analytical (e.g., BW) purposes.
• @UI.lineItem — Designates the way the fields will be displayed in the Fiori list reports.
• @AccessControl.authorizationCheck: #CHECK — Ensures CDS Access Control (DCL).
• @OData.publish: true — When this CDS view is published, it automatically publishes the CDS view as an OData service.
• @Semantics.amount.currencyCode — Designates a field as a monetary value and associates it with a currency field.

9. What is a CDS Table Function and what would be your reason for using it?

A CDS table function is a method that uses ABAP Managed Database Procedures (AMDP) to integrate CDS and SQL (the HANA database) through logic that exists within the CDS view. It is necessary to develop a HANA database view with a table function that:

• Permits the implementation of logic on the HANA database that is too complex to be defined using CDS DDL (Data Definition Language) syntax.
• Requires the implementation of on the HANA database logic that iterative or procedural operations be performed.
• Requires the consumption of complex HANA calculations and treat them as a standard CDS view.
• Where the implementing method requires the use of the BY DATABASE FUNCTION FOR HDB LANGUAGE SQLSCRIPT iterative operations be performed.

10. What distinguishes @AbapCatalog.sqlViewName from a CDS view name?

The name after DEFINE VIEW in a CDS view is the name given to the view that is recognized within ABAP entities (i.e., ABAP programs and other CDS views). On the other hand, the @AbapCatalog.sqlViewName specifies the name of the underlying SQL view object within the ABAP Data Dictionary (SE11). Both names are obligatory, mutually exclusive, and are needed for different functions.

• The CDS view is needed in ABAP SELECT statements and CDS associations.
• The SQL view name is the underlining physical object that is exposed in the database catalog and SE11.

11. Explain what secondary indexes are and their relevance in SAP HANA?

Secondary indexes are created on columns that are frequently filtered on, or used in joins, in order to improve the performance of SELECT queries. SAP HANA reduces the need to have secondary indexes because data is stored in a compressed column format and is loaded into memory. This means that SAP HANA is able to achieve full column scans of tables very quickly. Even with this, secondary indexes in SAP HANA make sense in scenarios like:

1. Queries on non-primary-key columns that are highly selective
2. The need for expression of a unique constraint
3. The need for optimization of very large tables with selective point lookups

ABAP developers working in the SAP HANA environment need to consider code pushdown over index strategies.

12. What is the NEW OPEN SQL syntax introduced in SAP ABAP on HANA?

The addition of a new Open SQL syntax pushes the limits of HANA and improves the SQL standards. The new syntax improves the following:

• @variable inline host variable declarations
• INTO TABLE @DATA(lt_result) — inline data declarations in SELECT
• Support for GROUP BY and HAVING in Open SQL
• Support for the string functions: CONCAT, SUBSTRING, LENGTH, UPPER, LOWER in Open SQL
• Support for arithmetic expressions in SELECT
• Support for Open SQL CASE statements
• Support for set operations UNION, INTERSECT, and EXCEPT
• Support for SELECT DISTINCT

For example, the following SQL syntax is supported:

SELECT
  matnr,
  maktx,
  COUNT(*) AS cnt
FROM makt
WHERE spras = @sy-langu
GROUP BY matnr, maktx
INTO TABLE @DATA(lt_materials).

13. What is an Access Control (DCL) in CDS and why is it important?

With the SAP CDS, it uses the Data Control Language (DCL) to set authorization standards for CDS views. It limits the data that a user is permitted to read from an authorization object without having to implement a custom authorization check in ABAP programs.

A DCL source is defined by a DEFINE ROLE in ADT and is automatically enforced at runtime when the CDS view is invoked. This refers to the authorization centrals at the dismissal of the manual AUTHORITY-CHECK statements on all ABAP programs that utilize the view.

14. What performance anti-patterns should be avoided during ABAP development on S/4HANA?

It's important to understand these anti-patterns because they are a common question in SAP ABAP on HANA interviews. Here are some of the more common anti-patterns in ABAP development:

1. SELECT * without field restrictions: Don't fetch the whole table. Only fetch what you need.
2. SELECT inside a LOOP: This is the classic "1+N" problem. Abandon the IN/OUT approach, and use JOINs, or move the table to the FOR ALL ENTRIES statement.
3. Nested SELECTs inside a LOOP: Nested SELECTs inside a LOOP need to be replaced with a single JOIN, or a CDS view.
4. SORT and DELETE ADJACENT DUPLICATES on large internal tables: This needs to push to the database using GROUP BY or DISTINCT.
5. PUSH ABAP Aggregation functions SUM, COLLECT: GROUP BY on the database.
6. Using views that contain OUTER JOINS, WHERE-clause filters: This is likely to prevent the HANA optimizer.

15. Describe the SAP HANA SQL Execution Engine and ABAP's role within the SQL Execution Engine.

SAP HANA has the Row Store Engine and the Column Store Engine, which are the two main Processing Engines. ABAP on HANA, in most cases, uses the Column Store Engine through the Open SQL, and ABAP Managed Database Procedures. In Open SQL, once the ABAP developer has created the ABAP Open SQL statement, the statement is translated into HANA SQL by the ABAP kernel, and the SQL statement is handed over to the HANA SQL processor. In an ABAP Managed Database Procedure, the SQL Script Procedure is run completely in the HANA Calculation Engine, which is ultimately bypassing the Application Server, in the case of an AMDP.

16. How do the AMDP Methods and CDS Table Functions differ?

17. What kind of architecture does the Virtual Data Model (VDM) for SAP S/4HANA have, and what does it imply for ABAP developers?

The VDM in SAP S/4HANA is a semantic, layered architecture over the S/4HANA database. Consisting of basic, composite, consumption, and extension views, VDM follows strict naming conventions (e.g., I_ for interface views, C_ for consumption views).

For ABAP developers, the VDM is essential because:

• Custom extensions are required to be built on VDM views and not on the database tables.
• It guarantees upgrade support.
• Standard CDS views are implied.
• OData services and Fiori apps are built with VDM consumption views.