📘 SAP ABAP – Internal Tables: Interview Questions & Answers

✅ 1. How to delete duplicates from an internal table?

• Use DELETE ADJACENT DUPLICATES FROM i_tab after sorting.

• Use COMPARING to restrict which fields determine duplicates.

🔹 Example:

SORT i_tab BY matnr werks logort.
DELETE ADJACENT DUPLICATES FROM i_tab COMPARING matnr werks.

✅ 2. What are the types of internal tables?

1. Standard Tables – Linear index, slower for large data.

2. Sorted Tables – Maintains order, binary search, fast read by key.

3. Hashed Tables – No index, uses hash algorithm, fastest for key-based access.
   
   

✅ 3. What is the size of an internal table?

• Controlled using OCCURS n (commonly OCCURS 0).

• Memory is allocated dynamically as entries increase.

• Affects performance, not actual size.
  
  

✅ 4. What is the effective way of using internal table records?

• Define internal table without header line.

• Use a work area to perform operations.

• Always CLEAR the work area after use.
  
  

✅ 5. Explain Sorted Tables.

• Entries inserted in sorted order using INSERT.

• Uses binary search.

• Duplicate keys not allowed.

• Best for partially sequential processing.
  
  

✅ 6. What is the difference between internal table and structure?

• Internal Table holds multiple records.

• Structure holds a single record during runtime.
  
  

✅ 7. What are field groups and internal tables?

• Field Group: Logical group of similar fields.

• Internal Table: Temporary memory used to store records at runtime.
  
  

✅ 8. What is SAP internal table key?

• Identifies rows; can be:

  • Standard Key

  • User-defined Key

• Keys can be UNIQUE or NON-UNIQUE.

• Sequence of key fields matters for sorting and performance.
  
  

✅ 9. Explain Hashed Tables.

• Best for key-based access.

• Constant response time regardless of size.

• Cannot access by index.

• Must have a unique key.
  
  

✅ 10. What do you mean by table types?

• Defines how data is accessed (index/key/hashed).

• Types: Standard, Sorted, and Hashed.

• Selection depends on performance and access needs.
  
  

✅ 11. What are control levels in internal tables?

Used in LOOPs:

1. AT FIRST

2. AT NEW

3. AT END OF

4. AT LAST

5. ON CHANGE OF



✅ 12. How can you specify internal tables as data objects?

• Defined by line type, key, and access method.

• Dynamic in size.

• Memory limit ≈ 2 GB (500 MB realistic).

• Hashed tables: Max ~2 million entries.
  
  

✅ 13. What is a generic internal table?

• Key or line type can be unspecified.

• Used for field symbols or interface parameters.

• Cannot declare regular data objects this way.
  
  

✅ 14. Explain Standard Internal Tables.

• Ideal for index-based operations.

• Use APPEND, READ INDEX, MODIFY INDEX, etc.

• Linear access time, can use binary search if sorted.
  
  

✅ 15. Explain:

• Internal Table: Runtime-only table in memory.

• Value Table: Domain-level validation.

• Check Table: Field-level validation (foreign key).

• Transparent Table: Same structure in DB and ABAP Dictionary.
  
  

✅ 16. How to choose a table type?

• Depends on access pattern:

  • Frequent index access → Standard Table

  • Sorted inserts → Sorted Table

  • Key-only access → Hashed Table
    
    

✅ 17. What is row type and line type?

• Line Type: Structure of each row (data type).

• Row Type: Actual content (data instance).

• Helps in reuse and DDIC-defined tables.
  
  

✅ 18. Difference between internal table and work area?

Feature	Internal Table	Work Area
Purpose	Holds multiple records	Single data row holder
Use	Store/loop/modify/delete data	Move data to/from table rows

✅ 19. Difference between database tables and internal tables?

Aspect	Database Table	Internal Table
Storage	Stored in DB Server	Runtime memory (App server)
Lifetime	Permanent	Temporary (during program run)
Access	Persistent SQL operations	SAP program operations

✅ 20. Difference between COLLECT and APPEND?

• APPEND: Adds row unconditionally.

• COLLECT: If duplicate key exists, sums numeric fields instead of appending.