Sybase 12.4.2 Improving your queries, Deciding to denormalize, Tips for structuring queries, 456

Improving your queries

Deciding to denormalize

When deciding whether to denormalize, you need to analyze the data access requirements of the applications in your environment and their actual performance characteristics. Some of the issues to examine when considering denormalization include:

•What are the critical queries, and what is the expected response time?

•What tables or columns do they use? How many rows per access?

•What is the usual sort order?

•What are concurrency expectations?

•How big are the most frequently accessed tables?

•Do any processes compute summaries?

•Should you create join indexes to gain performance?

Improving your queries

This section discusses several ways to improve queries for better performance, including:

•Tips on how to structure your queries to avoid operations that may be time consuming

•Suggestions for using the query plans Adaptive Server IQ provides

•Options you can set to modify query processing

Tips for structuring queries

Here are some hints for better query structure:

•In some cases, command statements that include subqueries can also be formulated as joins and may run faster.

•If you group on multiple columns in a GROUP BY clause, list the columns by descending order by number of unique values. This will give you the best query performance.

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