How can you optimize SQL queries with query rewriting and refactoring?

1 What is query rewriting and refactoring?

Query rewriting and refactoring are techniques for modifying the structure and logic of SQL queries without changing their functionality or results. The goal is to make the queries more readable, maintainable, and efficient. Query rewriting involves changing the syntax, keywords, or operators of a query to use a more optimal or standard form. Query refactoring involves changing the design, organization, or decomposition of a query to use a more modular or reusable form.

2 Why optimize SQL queries with query rewriting and refactoring?

Optimizing SQL queries with query rewriting and refactoring can provide numerous advantages for database administration and development. For instance, you can expect faster query execution due to reduced data processing, disk I/O, network traffic, and memory usage. Additionally, queries can be made more clear, consistent, and concise to avoid errors or ambiguities. Furthermore, queries can become more modular, generic, or adaptable to avoid duplication or hard-coding and make them more reusable. All of these benefits can lead to improved response time and throughput of queries as well as better overall database system performance.

3 How to rewrite SQL queries for optimization?

When rewriting SQL queries for optimization, there are many approaches to consider depending on the context. Generally speaking, it's important to use the most appropriate join type, such as inner join, left join, or right join, in order to minimize the number of rows and columns involved in the join operation. Indexes and constraints can also be used to enforce data integrity and facilitate data retrieval. Subqueries and common table expressions (CTEs) can simplify the query logic and structure but should be used judiciously as they could introduce overhead or complexity. All these tips can help speed up query execution for filtering, sorting, grouping, inserting, updating, or deleting operations.

4 How to refactor SQL queries for optimization?

When refactoring SQL queries for optimization, there are many approaches to consider depending on the specific situation and context. Generally speaking, functions and procedures should be used wisely to enhance query functionality and maintainability. Views and materialized views can improve query abstraction and security, but should be used carefully. Additionally, query hints and options can improve optimization and execution, but should be used sparingly. When using these approaches, it is important to consider any potential overhead or complexity that may be introduced.

5 What are some best practices for query rewriting and refactoring?

Query rewriting and refactoring are not one-size-fits-all solutions, and they may have different effects or outcomes depending on the database system, data model, query workload, or performance goal. Therefore, you should always follow some best practices for query rewriting and refactoring. It is essential to analyze and measure your queries before and after rewriting or refactoring them, using tools such as explain plans, execution plans, query statistics, performance monitors, or benchmarks. Additionally, it is important to test and validate their functionality and results with techniques such as unit testing, integration testing, regression testing, or data quality checks. Moreover, when rewriting or refactoring your queries you should follow coding standards and conventions for SQL queries in order to improve the query readability and consistency. This can help avoid errors, confusion, or conflicts in your queries.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?