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Is it slow to use order by in SQL?
Order by on an indexed field should not be slow as it can pull the data in index order. You might want to put up information about the database structure (the DDL) and the actual query so people can take a look. You absolutely should use a SQL sort rather than a code sort where possible so you are on the right track there.
What should be the slowness of SQL Server?
If 50 A rows match and 50 B rows match, you’ll end up with 2500 result rows, which may not be what you intend. It shouldn’t be slow. Optimize your query and database structure (at least indexes and statistcs if it’s SQL Server).
Is it efficient to sort by limit in MySQL?
Beware of large LIMIT Using index to sort is efficient if you need first few rows, even if some extra filtering takes place so you need to scan more rows by index then requested by LIMIT. However if you’re dealing with LIMIT query with large offset efficiency will suffer.
Which is slower limit 1000 or limit 10?
However if you’re dealing with LIMIT query with large offset efficiency will suffer. LIMIT 1000,10 is likely to be way slower than LIMIT 0,10. It is true most users will not go further than 10 page in results, however Search Engine Bots may very well do so.
How is the Order of mysql table satisfied?
Assuming that the table is InnoDB, by starting the PK with updated_at, the WHERE and ORDER BY are both satisfied by a “range” scan of the data. And only part (about half) of the table needs to be scanned. Profiling is essentially useless. 99% of the time is spent in the meaningless “Sending data” or one or two other cryptic phases.
How long does it take to execute a query in MySQL?
I can execute this query, which takes 15 seconds approximately: And this is the same query but adding an order by:
What happens when you have both limit and order by Foo?
When you have both the LIMIT and ORDER BY, the optimizer has decided it is faster to limp through the unfiltered records on foo by key descending until it gets five matches for the rest of the criteria. In the other cases, it simply runs the query as a nested loop and returns all the records.
How to make a SQL query run faster?
If you’re quering just a few simple columns (2-4), you can include them into the index as well. This way your query will be ran faster. Also make sure that sorting order on that index column matches sorting order in your query. Create a view and bind it to the schema. Then query data from that view.
Where does the slowness come from in SQL?
I suspect slowness comes from ” A.PREVIOUS <> ‘N’ OR A.PREVIOUS IS NULL” Try using (NOT A.PREVIOUS = ‘N’) which I think is equivalent and may help a bit. Time the query with and without the ORDER BY and see if the timing is at all different.