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What is join order optimization?
If the join query with ordering or grouping is processed in one step, the table with the ordering or grouping columns is the primary table. Determine an access method, cost, and expected number of rows returned for each join combination of candidate tables as primary and first secondary tables.
Does the order of join matter?
The order doesn’t matter for INNER joins. Outer joins are not commutative. Therefore, a LEFT JOIN b is not the same as b LEFT JOIN a. Outer joins are not associative either.
What does the join Order of my tables matter?
SQL Server will interpret and optimize our three separate queries (plus the original one from the top of the page) into the same exact execution plan: Basically, no matter how we try to redefine the order of our tables in the FROM statement, SQL Server will still do what it thinks it’s best. But what if SQL Server doesn’t know best?
How to optimize mysql query with many joins?
It doesn’t appear that you are using any fields in any of the joined tables, so remove the joins. This will remove all of the additional work of the query, and get you down to one, simple execution plan (one line in the EXPLAIN result). Each JOINed table causes an additional lookup per row of the result set.
Do you have control over the join order in SQL Server?
By default SQL Server gives you no control over the join order – it uses statistics and the query optimizer to pick what it thinks is a good join order. Most of the time, the query optimizer does a great job at picking efficient join orders.
When to use left join or right join in SQL?
At worst it could force the query optimiser to sort the result set before joining; and that is not necessarily good for the query plan. Rather only apply ordering right at the end for final display. Use of LEFT JOIN in your subqueries is inappropriate.