Types of Internal Tables in ABAP
Internal tables are a crucial part of ABAP programming,
allowing developers to handle large amounts of data efficiently in-memory.
1. Types
of Internal Tables
In ABAP, internal tables are classified into two main
types based on how they manage data and their performance characteristics:
a. Indexed
Internal Tables
- Standard Internal Tables
- Sorted Internal Tables
b. Hashed Internal
Tables
Standard
Internal Table
A standard internal table is the most basic type of
internal table. It is called "standard" because it behaves like a
simple list of entries.
Key Characteristics:
1. Allows duplicate records: You can store the same
record multiple times.
2. Non-unique fields: All fields can be non-unique,
meaning no field is required to be distinct.
3. Data insertion: Data is added to the table using the APPEND
keyword, which adds records to the end of the table.
4. Linear search: Searching for records in a standard
internal table is performed using a linear search, meaning the system checks
records one by one, which can be slower for large datasets.
Syntax:
ABAP
DATA: it_standard
TYPE STANDARD TABLE OF <structure>.
Sorted Internal Table
A sorted internal table is an internal table where
records are automatically sorted based on a key when inserted.
Key Characteristics:
1. May or may not allow duplicates: You can choose
whether to allow duplicate records based on the key.
2. Unique or non-unique fields: At least one field must
be specified as a key, which can be either unique or non-unique.
3. Data insertion: Data is added using the INSERT
keyword, which places records in the correct position to maintain sorting.
4. Binary search: Records are searched using a binary
search, making searches faster, especially with large datasets.
Syntax:
ABAP
DATA: it_sorted TYPE
SORTED TABLE OF <structure> WITH UNIQUE/NON-UNIQUE KEY <field>.
Hashed Internal Table
A hashed internal table is designed for fast access to
records based on a key.
Key Characteristics:
1. Does not allow duplicates: Only unique records can be
stored.
2. Unique fields: You must specify at least one unique
field.
3. Data insertion: Data is added using the COLLECT
keyword, which handles numeric fields in a special way. If a record already
exists, numeric fields are added up, otherwise, the record is appended.
4. Hash algorithm search: Searches are performed using a
hash algorithm, making access extremely fast.
Syntax:
ABAP
DATA: it_hashed TYPE
HASHED TABLE OF <structure> WITH UNIQUE KEY <field>.
Internal Table with Header Line
In older versions of ABAP, it was common to declare an
internal table with a header line. This means the internal table automatically
comes with a work area of the same name. This is no longer recommended, but
it’s still seen in legacy code.
Operations on Internal Tables
Once an internal table is defined, there are several
common operations you can perform on it:
a. Pushing Data
(Inserting Data)
- Append: Adds a record to the end of a standard internal
table.
ABAP
APPEND <wa> TO <it_standard>.
- Insert: Inserts a record in the correct position for a sorted
internal table or simply adds it to the end in a standard internal table.
ABAP
INSERT <wa> INTO TABLE
<it_sorted>.
- Collect: Adds a record to a hashed internal table. If a
record with the same key exists, numeric fields are summed.
ABAP
COLLECT <wa> INTO <it_hashed>.
b. Reading Data
You can read records from an internal table in two ways:
- Single record: Use READ TABLE to fetch one record.
- Multiple records: Use LOOP AT to iterate over the
entire table.
c. Modifying Data
You can change records in an internal table using the MODIFY
keyword.
d. Deleting Data
Records can be removed from an internal table using the DELETE
keyword.
e. Sorting Data
Internal tables can be sorted using the SORT keyword.
This operation is useful for standard tables where you need to order records
manually.
7. Key Differences Between Internal Table Types
|
Feature |
Standard Table |
Sorted Table |
Hashed Table |
|
Duplicates |
Yes |
Optional |
No |
|
Key Requirement |
No |
Yes (unique or
non-unique) |
Yes (unique) |
|
Insertion Method |
APPEND |
INSERT |
COLLECT |
|
Search Method |
Linear Search |
Binary Search |
Hash Algorithm |
|
Performance |
Slow for large data |
Moderate |
Fast |
Internal tables are a powerful tool for handling data
in-memory in ABAP. Understanding the differences between standard, sorted, and hashed
internal tables can help you choose the right table type for your needs.
Whether you need fast searching, unique records, or sorted data, internal
tables offer flexible options to make your ABAP programs more efficient.