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WHY IS LEFT join faster?
I’ve experienced some cases where a left join has been faster than a inner join. The underlying reason is this: If you have two tables and you join on a column with an index (on both tables). If the optimizer chooses to optimize the left join in the order it is written it will perform better than the inner join.
Which is faster WHERE or inner join?
A Subquery or Inner query or Nested query is a query within SQL query and embedded within the WHERE clause. The subquery can be placed in the following SQL clauses they are WHERE clause, HAVING clause, FROM clause. Advantages Of Joins: The advantage of a join includes that it executes faster.
Are outer joins bad?
It is an anti-join of sorts. It is not that outer joins are ALWAYS slower — it is that outer joins preclude the consideration of many access plans and therefore stand a chance of being significantly slower.
Which is faster, an outer join or an inner join?
A LEFT JOIN is absolutely not faster than an INNER JOIN. In fact, it’s slower; by definition, an outer join (LEFT JOIN or RIGHT JOIN) has to do all the work of an INNER JOIN plus the extra work of null-extending the results.
Why is left join slower than inner join?
The LEFT JOIN query is slower than the INNER JOIN query because it’s doing more work. From the EXPLAIN output, it looks like MySQL is doing nested loop join. (There’s nothing wrong with nested loops; I think that’s the only join operation that MySQL uses in version 5.5 and earlier.)
How to optimize inner join in SQL Server?
BUT, the optimizer may also optimize a left join sub-optimally as a left semi join. To make it choose the one you want you can use the force order hint. Try both queries (the one with inner and left join) with OPTION (FORCE ORDER) at the end and post the results.
What happens if you add an index to an inner join?
If you were to add an index (is it really varchar, btw? not numeric?) on that, your INNER JOIN might behave differently (and become faster) as well. The INNER JOIN has to do an extra check to remove any records from A that don’t have matching records in B and C. Depending on the number of records initially returned from A it COULD have an impact.