Every ABAP system runs on a relational database management system (DBMS). Technically, ABAP supports different database management systems from different vendors.
In a relational database, information is stored in two-dimensional tables, in which each row represents one data record whose contents are split up into columns. The database is called a relational database, as there are also relations between tables. For example, the table in the figure contains an airline code. In the database table, there would be a relationship to a further table containing the information that AA stands for American Airlines, JL for Japanese Airline, LH for Lufthansa, and so on.
A sequence of columns at the beginning of each database table forms its key. The key is a combination of values that ensures that each row in the table can be identified uniquely.
Database tables in SAP systems are repository objects, and as such, are cross-client. However, the vast majority of tables contain business data, which is client-specific. To keep the data separate, client-specific tables have a client field (often named CLIENT or MANDT) as their first key field. The database of SAP accesses statements using ABAP SQL to ensure that a statement only manipulates data from the current client.
Database Table Definitions
ADT provides a dedicated editor for database table definitions.
Let's look at the different parts of the table definition.
Data Preview for Database Tables
You can use the Data Preview tool to display and analyze the content of a database table. To open the Data Preview for a given table, right-click anywhere in the table definition and choose Open With > Data Preview. Alternatively, place the cursor anywhere in the database table definition and press Ctrl + F8.
The tool displays the data stored in the database table. Some of the most important functions are shown here.