The SQL Optimizer module automates the optimization of SQL statements. It employs a unique engine that uses Artificial Intelligence to generate all the possible SQL alternatives that can be mathematically proven to be "semantically equivalent" to the original SQL statement which guarantees that the SQL alternatives will produce the exact same results as the original SQL statement. After the alternatives are generated, you can compare each SQL statement to any other SQL statements to see the different SQL coding techniques for achieving the same results. You can then test these alternative SQL statements in your environment to find the best one for your database environment.
The first step of this engine transforms the original SQL statement and produces a group of alternative SQL statements where the syntax was rewritten. Then, the SQL Optimizer rewrites each newly created SQL statement to produce another group of alternatives. The engine continues rewriting each alternative until all the SQL statements cannot be rewritten any further or until the user-defined quota for the number of SQL statements generated by syntax transformation is reached.
In the Optimization settings, you can also control whether the optimization process will generate SQL statements make use of temporary tables. You can also select to use the JOIN clause (INNER JOIN, CROSS JOIN) from the Ansi-92 SQL standard or to use the original SQL syntax for joining tables.
After the SQL Optimizer has exhausted rewriting the syntax of the SQL statement, the various techniques available in Adaptive Server for optimizing a SQL statement are applied to the original SQL statement and each of the SQL alternatives until all selected options have been applied to all the SQL alternatives or until the user-defined quota is reached.
For each rewritten SQL statement, the query plan is compared to all the other query plans. One SQL alternative is selected for each unique query plan. Although the optimization process may generate hundreds of SQL alternatives, you will see only some of the alternatives since the alternatives with a duplicate query plan are eliminated.
Although all the SQL alternative statements produce the same result, Adaptive Server will likely use a different path to retrieve the data for each one. It is difficult to decide which SQL statement will run faster without taking into account the database structure, indexes, and data volume, so it is important to test the SQL alternatives in your database environment using the Batch Run to determine the best SQL alternative from the run time statistics.
The settings in the Optimizer options affect the amount of time it takes and the number of alternatives that are generated by the optimization process. You can quickly select to increase or decrease the intensity of the optimization process using the Intelligence Level settings to automatically select more or less options.
You also have the ability to test and compare your own SQL alternatives using the Insert User-Defined SQL function.
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