This blog is the fourth in a series about misconceptions surrounding SQL tuning that are quite common. It covers the misconception that the goal of SQL tuning is only to make a SQL return all the records faster.

I still remember around 20 years ago, I was using SQL*Plus to tune my SQL statements. At that time, it was my impression that a good SQL rewrite was one that normally would return the ...

This blog is the second in a series about common misconceptions surrounding SQL tuning. It covers the misconception that the goal of SQL tuning is to write a better SQL statement. The real goal of SQL tuning is not to create a better SQL statement, but it is to help the database optimizer to make the right decision when it is choosing the execution plan.

If you browse the internet with the key ...

Written by Rene Woody

This blog is a continuation of a series about the SQL optimization process in the Batch Optimizer and the Tuning Lab modules of Quest SQL Optimizer for Oracle. It explains the order in which the SQL stateme ...

Written by Rene Woody

Recently, I received an email from the presales support team. They asked me to help them tune three SQL statements for a benchmark database provided by a customer. Our presales support said that our SQL Optimizer was not providing any alternatives for two of these three complex SQL statements. I found two of these SQL statements were very complicated and I knew that there should be a lot of alternative SQL genera ...

“Why does adding a ||'' to the end of a key value improve performance... in this case significantly, this query runs in 187 milliseconds regularly where without the ||'' it takes minutes to run... This is the only modification in the result set from SQ ...

There are at least two database vendors are trying to build self-learning SQL optimizers. The idea is to use actual statistics from executed SQL statements to rectify the future cost estimation of the same or similar SQL statements. It seems like a good idea, but, you will find that their existing self-learning ...

Be sure to read

To read part one in this series on O ...

Quest Recursive SQL Transformation technology is an innovative AI technology that simulates human SQL transformation technique. It incorporates a set of transformation rules to transform SQL statements on a section-by-section basis. This replaces the trial and error method used by human to rewrite the syntax of a SQL statement. Each t ...

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I have been asked many times that why there are some dummy SQL transformations/rewrites that look meaningless, but it works in certain situations.  Let me give you some examples that may help to explain what theory on behind of Quest SQL Optimizer.

In Quest SQL Optimizer, transformation rules relating to index usage are designed to guide the database SQL optimizer as to how it should use the indexes for a specific SQL statement.  Although those rules may familiar to most of SQL developers, but it is still worth to illustrate some commonly used rules for SQL beg ...

In old version of Oracle database, it is easy to control the join path by reordering the tables in table list after the FROM clause, but it is getting difficult to control the join path in today’s cost based SQL optimizer, I am going to introduce method that is applicable in most databases such as Oracle, Sybase, DB2 and SQL Server in the following:

To control a join path, we cannot tell the database SQL optimizer which path is the best one to select. Instead, we add something to the syntax of the SQL statement that causes an increase to the cost of the current join path selected by database SQL optimizer. Let’s take a look at the following example of two table join scenarios.