WHY IS LEFT join slower?

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.

Is left outer join slower than 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.

How can I improve my left join performance?

And if you do multiple LEFT JOINs, then you could (probably) separate them into different queries and this should make the application work a lot faster. You can refer to the MySQL’s documentation on optimization, specifically LEFT JOIN optimization and optimization using indexes. This may give you additional details.

How do you optimize left join in SQL?

Try creating an index and see if it is faster. For further optimisation, you can use SQL’s EXPLAIN to see if your query is using indexes where it should be. Try http://www.dbtuna.com/article.asp?id=14 and http://www.devshed.com/c/a/MySQL/MySQL-Optimization-part-1/2/ for a bit of info on EXPLAIN.

IS LEFT join faster than full outer join?

However, if you change the matching key in the join query from Name to ID and if there are a large number of rows in the table, then you will find that the inner join will be faster than the left outer join.

How do I speed up a join query?

Answers

  1. Always reduce the data before any joins as much possible.
  2. When joining, make sure smaller tables are on the left side of join syntax, which makes this data set to be in memory / broadcasted to all the vertica nodes and makes join faster.
  3. Join on INT columns, preferred over any other types, it makes it faster.

Does Outer join affect performance?

Outer join will normally give you MANY more results ( A*B instead of WHERE A=B ). That’ll take more time. An outer join will not normally give you A multiplied by B as the number of results as it isn’t a union.

Is left outer join faster than inner join?

Returns only the rows that have matching values in both the tables. Includes the matching rows as well as some of the non-matching rows between the two tables. In case there are a large number of rows in the tables and there is an index to use, INNER JOIN is generally faster than OUTER JOIN.

Do joins slow down query?

Joins: If your query joins two tables in a way that substantially increases the row count of the result set, your query is likely to be slow. There’s an example of this in the subqueries lesson. Aggregations: Combining multiple rows to produce a result requires more computation than simply retrieving those rows.

IS LEFT join faster than inner?

If the tables involved in the join operation are too small, say they have less than 10 records and the tables do not possess sufficient indexes to cover the query, in that case, the Left Join is generally faster than Inner Join. As you can see above, both the queries have returned the same result set.

Does LEFT join take more time than 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. It would also be expected to return more rows, further increasing the total execution time simply due to the larger size of the result set.

How make MySQL join faster?

Originally Answered: can I make my JOIN on big tables faster in MySQL? One item: if possible, use InnoDB storage engine on these tables. It executes joins on the PK much, much faster than MyISAM, which has to use secondary storage for PK and does a key to record indirection for each rec.