Why is MY SQL Server order by slow despite the ordered?

Why is MY SQL Server order by slow despite the ordered?

The important line seems to be “|–Sort (ORDER BY: ( [mydb]. [dbo]. [jobs]. [issueDatetime] ASC))” — without any mention of an index on that column. Why is my ORDER BY making my query so much slower, and how can I speed up my query? If your query does not contain an order by then it will return the data in whatever oreder it was found.

How to make SQL query a lot faster?

If you want to make your query a lot faster, then reverse the order of your tables. Specifically, list table country first in your joined tables. The reason why this helps is that the where clause can filter rows from the first table instead of having to make all those joins, then filtering the rows.

What happens if the query does not contain an order?

If your query does not contain an order by then it will return the data in whatever oreder it was found. There is no guarantee that the data will even be returned in the same order when you run the query again.

Can a non-clustered index be used to improve order by performance?

I can speed it up dramatically by adding a clustered index on the column in the ORDER BY clause. However, the software creates the query to order by different columns, depending on user settings. And you cannot add more than one clustered index to a table. My question is: can non-clustered indexes be used to improve ORDER BY performance?

What to do if your SQL Server query is slow?

If you use SQL Server 2005 and obove, you can also try to run you query in SQL Server Profiler and it will recommend to you the best index and statistics which you can apply to your table in order to optimize this particular query’s performance. Try to rebuild your indexes and statistics.

How does an ORDER BY clause affect the query plan?

An ORDER BY clause can affect the query plan, because if there is an index that can provide the results in the order that matches the ORDER BY clause, then the optimizer may choose to use it. Because of that, the access order may change, which means most of the query plan will change.

How long does a SQL query take without an order?

Unfortunately it also takes ~16 seconds. Without the ORDER BY, the query takes <1 second.

Which is the correct index for merge join?

Judging from the sp_spaceused output ‘a couple of GB’ might be quite an understatement – the MERGE join requires that you trawl through index which is going to be very I/O intensive. Your index is incorrect. See indexes dos and donts. As things stand, your only useful index is that on the small table’s primary key.

How to merge small table with huge table?

The only reasonable plan is thus to seq scan the small table and to nest loop the mess with the huge one. Try adding a clustered index on hugetable (added, fk). This should make the planner seek out applicable rows from the huge table, and nest loop or merge join them with the small table.