We always get confused about the type of internal tables. So ABAP knows the three table types STANDARD, SORTED, and HASHED table. Each of these table types differs in the way they are declared, accessed, and changed during runtime.

Lets understand this with the help of an example

For the following declaration we use the local type ty_sales_order_item which has fields from sales order table and it’s decleration will look something like this

TYPES: BEGIN OF ty_sales_order_item,
         vbeln   TYPE vbeln,
         posnr   TYPE posnr,
         matnr   TYPE matnr,
         deleted TYPE boolean,
       END OF ty_sales_order_item.

Standard table

Accessed by referring to the table index (which is the quickest access method). Access time for standard table increases linearly with respect to the number of table entries. New rows are appended to the table. Individual rows are accessed by reading the table at a specified index value.

• Unsorted but can be sorted with SORT
• Access via table index and table key
• Default key because the table is a standard table

now if we have to declare an standard table it will look like this

DATA: sales_order_items TYPE STANDARD TABLE OF ty_sales_order_item WITH DEFAULT KEY.

Sorted Table

Most appropriate where the table is to be filled in sorted order. Sorted tables are filled using the INSERT statement. Inserted entries are sorted according to a sort sequence defined by the table key. Illegal entries are recognized as soon as you try to insert them into the table. Response time is logarithmically proportional to the number of table entries (since the system always uses a binary search). Sorted tables are particularly useful if you wish to process row by row using a LOOP.

• Sorted according to the defined table key
• Access via table index and table key
• Fast key access thanks to binary search
• Primary Key: table_line

	
DATA: sales_order_items TYPE SORTED TABLE OF string WITH UNIQUE KEY table_line.

Hashed Table

Most appropriate when access to rows is by a key. (Cannot access hashed tables via the table index)response time remains constant regardless of the number of rows in the table.

• Access only via a unique key, no index
• Each key value may only appear once, otherwise an exception is raised
• Fast if all key fields are included
• Primary Key: vbeln

	
DATA: sales_order_items TYPE HASHED TABLE OF ty_sales_order_item WITH UNIQUE KEY vbeln.

Defining keys for an internal table can play a significant role i.e. it determines how you entries will be processes and in which way, below is the recommendation from SAP

Hashed as well as sorted both has unique and non unique keys ( unique means only one key will be there, non-unique multiple entries for the key

key must be specified, Example see how data decleartion needs to be done

DATA : it_mat type sorted table of ty_mat with unique key matnr

DATA : it_mat type sorted table of ty_mat with non-unique key matnr

example:-

Here duplicate entries are not inserted

*&---------------------------------------------------------------------*
*& Report  ZSOTED_TABLE
*&
*&---------------------------------------------------------------------*
*&
*&
*&---------------------------------------------------------------------*
 
REPORT ZSOTED_TABLE.
 
TYPES : begin of ty_tab,
am TYPE i,
cou TYPE i,
END OF ty_tab.
 
DATA : it_tab TYPE SORTED TABLE OF ty_tab WITH UNIQUE KEY cou,
wa_tab TYPE                 ty_tab.
 
do 3 TIMES.
wa_tab-am = sy-index.
wa_tab-cou = sy-index + 1.
INSERT wa_tab INTO TABLE it_tab.
ENDDO.
 
wa_tab-am = sy-index.
wa_tab-cou = '3'.
INSERT wa_tab INTO TABLE it_tab.
 
loop at it_tab INTO wa_tab.
WRITE : / wa_tab-am,
wa_tab-cou.
ENDLOOP.

Generic Key Operations

Data Transfer & Internal Tables

Filling line by line

• Append, Collect, Insert

Copying the contents of another table

• Append, insert, move

Reading line by line

• Loop, read, search

Determining the attributes of an internal table

• Describe