I’m running these tests on SQL Server 2019 (.41) on an 8-core VM with 64GB RAM. For the sake of these tests, I’m not going to talk about isolation levels or blocking. There are also other ways to measure these methods depending on your own performance requirements: memory grants, ability to run without blocking, and even the accuracy of the results under concurrency. In your own environment, for the tables you’re trying to count and the hardware you’re using and the version you’re on and the phase of the moon, you’re going to get different results, and that’s fine. How much CPU time it uses (gauged with SET STATISTICS TIME ON)ĭon’t obsess over small differences between the operations – I’m writing this blog post fast & furious to show you the big-picture differences, and to show you how my thought process works when comparing the different operations.How many pages it reads (gauged with SET STATISTICS IO ON).Let’s do an exploration of the Votes table in the Stack Overflow database, specifically the 2018-06 ~300GB version where the Votes table has 150,784,380 rows taking up ~5.3GB of space. + "ON (t1.address = t2.address AND t1.date < t2.When you run a SELECT COUNT(*), the speed of the results depends a lot on the structure & settings of the database. + "LEFT OUTER JOIN messages_database t2 " "SELECT t1.*, COUNT(t1.message_content) AS count " + ") ss ON t.address = ss.address AND t.date = ss.maxdate", + " SELECT address, MAX(date) AS maxdate " "SELECT t.*, COUNT(t.message_content) AS count " The two queries were: Cursor cursor = db.rawQuery( How can I select the one latest message for each address without removing my GROUP clause (as COUNT() relies upon this)? Do I need two queries?Įdit: Based on the answer linked me to in the comments, I came up with two queries which both produced the same result one row, in which the count was 7 (which is the total number of addresses, not messages per address), and the address shown was not that of the latest message. Google searches have proved fruitless queries like " android sqlite order before group" and " android sqlite group by order" yield no related results. If I set my GROUP BY clause to be "address, date", then they are sorted by date, but of course they are all individual instead of grouped (since the dates differ). I tried setting my HAVING clause to "MAX(date)", but it had no effect. I've used MySQL a lot with PHP, but never had to touch HAVING before. I feel like this may have to do with the HAVING clause, but I really don't know. * SELECT */ new String, null, null, "address", null, "date DESC") Here is what I have so far: // Expanded version: It should fetch messages C and F, and sort those by date. The query may fetch messages B and E, then sort them by date. It appears to be arbitrary.Īs an example, I have three messages (earliest to latest) A, B, C from address Y, and three messages D, E, F from address Z. It fetches the correct count, fetches only one message per address, and orders them by date-but it does not select the most recent message for the address. So, I thought, "I can just GROUP by the address to only get one message per address, then ORDER these by the date, and also fetch the COUNT of the address column." What I want to do is select the first message's address, message, date, and how many messages are associated with the address. Each message also has a date associated with it. I have a SQLite database full of addresses and messages (addresses are not unique messages are).
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