In ABAP/4 programming language, there are two types of SQL being used.
NATIVE SQL OPEN SQL.
Open SQL allows you to access the database tables declared in the ABAP dictionary regardless of the database platform that the R/3 system is using. Native SQL allows you to use database-specific SQL statements in an ABAP/4 program. This means that you can use database tables that are not administered by ABAP dictionary, and therefore integrate data that is not part of the R/3 system. Open SQL consists of a set of ABAP statements that perform operations on the central database in the R/3 system. The results of the operations and any error messages are independent of the database system in use. Open SQL thus provides a uniform syntax and semantics for all of the database systems supported by SAP. ABAP programs that only use Open SQL statements will work in any R/3 system, regardless of the database system in use. Open SQL statements can only work with database tables that have been been created in the ABAP dictionary.
Basic Open SQL Commands
SELECT INSERT UPDATE MODIFY DELETE OPEN CURSOR, FETCH, CLOSE CURSOR
Example Output the passenger list for the Lufthansa flight 0400 on 28-02.1995:
Open SQL Return Codes
All Open SQL statements fill the following two system fields with return codes. SY-SUBRC After every Open SQL statement, the system field SY-SUBRC contains the value 0 if the operation was successful, a value other than 0 if not. SY-DBCNT After an Open SQL statement, the system field SY-DBCNT contains the number of database lines processed.
Native SQL
As already mentioned, Native SQL allows you to use database-specific SQL statements in an ABAP program. To use Native SQL statement, you must precede it with the EXEC SQL statement, and follow it with the ENDEXEC statement. Syntax There is no period after Native SQL statements. Furthermore, using inverted commas (“) or an asterisk (*) at the beginning of a line in a native SQL statement does not introduce a comment as it would in normal ABAP syntax. You need to know whether table and field names are case-sensitive in your chosen database. In Native SQL statements, the data is transported between the database table and the ABAP program using host variables. These are declared in the ABAP program, and preceded in the Native SQL statement by a colon (:). You can use elementary structures as host variables. Exceptionally, structures in an INTO clause are treated as though all of their fields were listed individually. As in Open SQL, after the ENDEXEC statement, SY-DBCNT contains the number of lines processed. In nearly all cases, SY-SUBRC contains the value 0 after the ENDEXEC statement.
Open SQL – Performance Rules
To improve the performance of the SQL and in turn of the ABAP program, one should take care of the following rules- Keep the Result Set Small
Using the where clause If only one record is required from the database, use SELECT SINGLE whenever possible .
Minimize the Amount of Data Transferred
Restrict the number of lines
If only certain fields are required from a table, use the SELECT
Minimize the Number of Data Transfers
Avoid nested select loops An alternative option is to use the SELECT .. FOR ALL ENTRIES statement. This statement can often be a lot more efficient than performing a large number of SELECT or SELECT SINGLE statements during a LOOP of an internal table.
Use dictionary views Use Joins in the FROM clause Use subqueries in the where clause
Minimize the Search Overhead
Use index fields in the where clause When accessing databases, always ensure that the correct index is being used .
Reduce the Database Load
Buffering Logical databases Avoid repeated database access
Using Internal Tables to Buffer Records
To avoid executing the same SELECT multiple times (and therefore have duplicate selects), an internal table of type HASHED can be used to improve performance.
