The attempt was made in this chapter to show the importance of optimal SQL statements and the ways in which these can be created. The descriptions given in this chapter should enable the user to find useful formulations for the enquiries. Before including these statements into a program, they can be checked for correctness within the ADABAS component QUERY and for the performance obtained by them by means of EXPLAIN statements.
If the user consequently follows the instructions given in this chapter from the very beginning, later tuning overhead, if any, should be minimal.
SQL is a powerful database query language, which can save an application quite a lot of work. But as shown by the last example in chapter Instructions to Increase the Speed , there are limits beyond which the performance of an application can be improved, not by expanding an SQL command, but by adding some additional lines of code to the application.