For example, I have the following table:
table Product
------------
id
category_id
processed
product_name
This table has index on columns id category_id and processed and (category_id, proccessed). The statistic on this table is:
select count(*) from Product; -- 50M records
select count(*) from Product where category_id=10; -- 1M records
select count(*) from Product where processed=1; -- 30M records
My simplest query I want to query is: (select * is the must).
select * from Product
where category_id=10 and processed=1
order by id ASC LIMIT 100
The above query without limit only has about 10,000 records.
I want to call the above query for multiple time. Every time I get out I will update field processed to 0. (so it will not appear on the next query). When I test on the real data, sometime the optimizer try to use id as the key, so it cost a lot of time.
How can I optimize the above query (In general term)
P/S: for avoiding confuse, I know that the best index should be (category, processed, id). But I cannot change the index. My question is just only related to optimize the query.
Thanks
Gordon Linoff :
For this query:\n\nselect *\nfrom Product\nwhere category_id = 10 and processed = 1\norder by id asc\nlimit 100;\n\n\nThe optimal index is on product(category_id, processed, id). This is a single index with a three-part key, with the keys in this order.",
2019-10-01T16:18:34