Internal table is actually a temporary table, which contains the records of an ABAP program that it is being executed. An internal table exists only during the run-time of a SAP program. They are used to process large volumes of data by using ABAP language. We need to declare an internal table in an ABAP program when you need to retrieve data from database tables.
Data in an internal table is stored in rows and columns. Each row is called a line and each column is called a field. In an internal table, all the records have the same structure and key. The individual records of an internal table are accessed with an index or a key. As internal table exists till the associated program is being executed, the records of the internal table are discarded when the execution of the program is terminated. So internal tables can be used as temporary storage areas or temporary buffers where data can be modified as required. These tables occupy memory only at run-time and not at the time of their declaration.
Internal tables only exist when a program is running, so when the code is written, the internal table must be structured in such a way that the program can make use of it. You will find that internal tables operate in the same way as structures. The main difference being that structures only have one line, while an internal table can have as many lines as required.
An internal table can be made up of a number of fields, corresponding to the columns of a table, just as in the ABAP dictionary a table was created using a number of fields. Key fields can also be used with internal tables, and while creating these internal tables they offer slightly more flexibility. With internal tables, one can specify a non-unique key, allowing any number of non-unique records to be stored, and allowing duplicate records to be stored if required.
The size of an internal table or the number of lines it contains is not fixed. The size of an internal table changes according to the requirement of the program associated with the internal table. But it is recommended to keep internal tables as small as possible. This is to avoid the system running slowly as it struggles to process enormous amounts of data.
Internal tables are used for many purposes −
They can be used to hold results of calculations that could be used later in the program.
An internal table can also hold records and data so that this can be accessed quickly rather than having to access this data from database tables.
They are hugely versatile. They can be defined using any number of other defined structures.
Assume that a user wants to create a list of contact numbers of various customers from one or several large tables. The user first creates an internal table, selects the relevant data from customer tables and then places the data in the internal table. Other users can access and use this internal table directly to retrieve the desired information, instead of writing database queries to perform each operation during the run-time of the program.