IS LEFT join better than subquery?

A LEFT [OUTER] JOIN can be faster than an equivalent subquery because the server might be able to optimize it better—a fact that is not specific to MySQL Server alone. So subqueries can be slower than LEFT [OUTER] JOIN , but in my opinion their strength is slightly higher readability.

Do subqueries reduce performance?

You can absolutely write a sub-query that performs horribly, does horrible things, runs badly, and therefore absolutely screws up your system. Just as you can with any kind of query. I am addressing the bad advice that a sub-query is to be avoided because they will inherently lead to poor performance.

Are left outer joins slow?

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. But LEFT JOIN will return all rows from a table specified LEFT and all matching rows from a table specified RIGHT.

Which is faster not in or left join?

Many years ago (SQL Server 6.0 ish), LEFT JOIN was quicker, but that hasn’t been the case for a very long time. These days, NOT EXISTS is marginally faster. The biggest impact in Access is that the JOIN method has to complete the join before filtering it, constructing the joined set in memory.

Which is faster LEFT OUTER JOIN or subquery?

A LEFT [OUTER] JOIN can be faster than an equivalent subquery because the server might be able to optimize it better—a fact that is not specific to MySQL Server alone. So subqueries can be slower than LEFT [OUTER] JOIN, but in my opinion their strength is slightly higher readability. @user1735921 IMO it depends

Where does the subquery go in a join query?

Most join queries contain at least one join condition, either in the FROM clause or in the WHERE clause. what is Subquery? A Subquery or Inner query or Nested query is a query within SQL query and embedded within the WHERE clause. A Subquery is a SELECT statement that is embedded in a clause of another SQL statement.

When to use left semi join or LEFT OUTER JOIN?

If a left-semi join is used then the optimizer rewrote the query. Even BOL says that correlated subqueries are processed row-by-row. For this type of query, the left join is more likely to get a hash/merge join, which translates into increased performance and consistency.

Which is easier to write joint or subquery?

A subquery is easier to write, but a joint might be better optimized by the server. For example a Left Outer join typically works faster because servers optimize it.