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@Roger Ray: have you actually tried what I suggested?
"can only help scan all the rows in table, which I'm trying to avoid" --- that's not entirely correct.
Using views in My SQL is not necessarily a "bad idea", but I would strongly caution those who choose to use views within My SQL to be AWARE of how My SQL processes queries that reference those views.
And the way My SQL processes view queries differs (significantly) from the way view queries are handled by other databases (e.g. If My SQL doesn't has a way to push the predicate from the outer query into the view query, it look like instead create a view execute specific query in particular circumstances is the best way to do it.@zerkms: I explain the use of the index on the second line as a result of the optimization for the GROUP BY.
It will help to avoid the table scan Of course I've tried what you suggested.
Instead of scan all 8 rows, with this composite index, it scanned 6 rows, then query with the condition of [happened_in = 2006].
Plus, creating a composite index in a table with large amount of data probably isn't a very good idea.
Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update).The way that view queries are processed may be "unexpected" by some, and this is one reason that using "views" in My SQL can lead to performance problems, as compared to the way view queries are processed by other relational databases.Improving performance of the view query with a suitable covering index Given your view definition and your query, about the best you are going to get would be a "Using index" access method for the view query. column, because that is the only other column referenced in your query.We needed a view to summarize data from 3 tables with over 3M rows overall. But I haven't found out a way to take advantages in the indexes in the conditional select statement retrieval from the view that we created with [group by]. column in the index will allow the query to satisfied entirely from the index, without having to visit (lookup) the data pages referenced by the index. The longer answer is that My SQL is very unlikely to use an index with leading column of Why the view causes a performance issue One of the issues you have with the My SQL view is that My SQL does not "push" the predicate from the outer query down into the view query. The My SQL optimizer does not consider the predicate when it runs the inner "view query".I've getting suggestions from people that using views in My Sql is not a good idea. That query for the view gets executed separately, before the outer query.
The leading columns in that index should be the columns that are referenced with equality predicates (in your case, the column operation, by making use of the index rather than using a sort operation.