SAP defines three main types of internal tables based on their structure and access method:

1. Standard Table (STANDARD TABLE)

• Default type if nothing is specified.

• Entries are stored unsorted (in the order you append them).

• Index-based access (like arrays).

• Duplicate entries allowed.

• Access time:

  • By index → very fast (O(1))

  • By key → linear search (O(n))

Use Case: Small-to-medium datasets where duplicates are needed, sequential processing.

DATA: it_mara TYPE STANDARD TABLE OF mara WITH DEFAULT KEY,
wa_mara TYPE mara.

SELECT * FROM mara INTO TABLE it_mara UP TO 10 ROWS.
READ TABLE it_mara INTO wa_mara INDEX 5. ” Access by index

2. Sorted Table (SORTED TABLE)

• Entries are always stored in a sorted order (by key).

• No need to SORT explicitly.

• Unique or non-unique keys possible (depending on definition).

• Binary search used internally for key access.

• Access time:

  • By key → fast (O(log n))

  • By index → slower than standard

Use Case: When you frequently read data by key and want it sorted automatically.

DATA: it_mara_sorted TYPE SORTED TABLE OF mara
WITH UNIQUE KEY matnr.

SELECT * FROM mara INTO TABLE it_mara_sorted UP TO 10 ROWS.
READ TABLE it_mara_sorted WITH TABLE KEY matnr = ‘MAT001’
INTO DATA(wa_mara).

3. Hashed Table (HASHED TABLE)

• Entries are stored in hash algorithm format (like a dictionary).

• Only unique keys allowed.

• No index access → can only be accessed via key.

• Access time: By key → constant (O(1)) on average.

• Best for large datasets when you always access by key.

Use Case: Fast key-based lookups, like material master lookup by MATNR.

DATA: it_mara_hashed TYPE HASHED TABLE OF mara
WITH UNIQUE KEY matnr.

SELECT * FROM mara INTO TABLE it_mara_hashed UP TO 1000 ROWS.
READ TABLE it_mara_hashed WITH TABLE KEY matnr = ‘MAT001’
INTO DATA(wa_mara).

Summary :