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Explicitly Disable Sorting of Result Set

· 2 min read
PawSQL Team
PawSQL Team
Optimize your SQL Queries by Clicks!

Copyright © 2024 PawSQL

Problem Definition​

In earlier versions of MySQL, GROUP BY would default to sorting by the grouping fields even without an ORDER BY clause. This could cause unnecessary file sorting which impacts SQL query performance. Adding ORDER BY NULL forces disabling sorting on the result set.

For example in the following:

SELECT l_orderkey, sum(l_quantity) 
FROM lineitem
GROUP BY l_orderkey;

Explain Visualization for MySQL

· 4 min read
PawSQL Team
PawSQL Team
Optimize your SQL Queries by Clicks!

Copyright © 2024 PawSQL

Overview​

The execution plan is an internal execution strategy generated by the database when executing SQL queries. It describes how the SQL is executed step-by-step internally in the database and is an important basis for diagnosing SQL performance issues and tuning. As the complexity of database applications increases, SQL execution plans become more and more complicated along with the SQL. Relying on plaintext execution plans makes it very challenging to grasp the overall execution plan, locate key paths and bottlenecks, bringing great difficulties to DBAs' performance tuning work.

The visual execution plan tool intuitively presents the execution plan in a flowchart, clearly showing the plan structure. It uses visual elements to highlight key operations and paths, while associating SQL statement source code for integrated analysis. This can greatly improve the efficiency for DBAs to understand and analyze execution plans, quickly locate performance bottlenecks, and perform precise optimization on SQL or indexes.