1/27/2024 0 Comments Mysql join order performance![]() ![]() Include actual execution plan while executing the following query: Let us try to check out the drawbacks of using SELECT * with AdventureWorks2014 sample database: ![]() The application might break, because of column order changes. ![]() SELECT * with WHERE conditions will use clustered index by default so it may not use optimal other indexes. When you SELECT *, it is possible to retrieve two columns of the same name from two different tables (when using JOINS for example). SELECT * Retrieves unnecessary data besides that it may increase the network traffic used for your queries. There are many reasons for that recommendation, like: When writing queries, it would be better to set the columns you need in the select statement rather than SELECT *. In the article, we will talk about the various operators and what do they do, when do they come and what happens. 80% of the work rules can benefit from the generalization but there is still 20% of particular specific used cases that the generalization might not be helpful. To make sure that we do not get into the realm of “it depends”, the whole article is mostly based on an 80-20 rule. We will be addressing the most common concepts which we often see that negatively impact SQL code written by developers. In this series, I will be discussing various aspects of query designing, keeping performance and scalability in mind. However, when writing code, the developer often lacks the knowledge and/or experience about SQL Server to meet this requirement. But to be honest, as a developer, it is your responsibility to write code which is efficient and optimal. Quite often developers put the responsibility of the server performance on the shoulders of DBAs. ![]()
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