Groupwise Max SQL Query Problem

I have a table that has following columns:

coin_id, data_item_id, rating, created_at

For each coin_id there's multiple rows from different data sources (marked with data_item_id), and rating from that data source.. but there are dozens of them. What I need is find the latest row for each data source (data_item_id) and get that row's rating. The output for example coin_id 32 should be:

rating: 69

69 is a SUM of ALL ratings from all "latest (determined by created_at column)" data sources.

If you undestand what I'm trying to say, or you have a concrete question ... bid and contact me, otherwise ..don't bother.

I won't hire somebody that thinks he can solve it (and if you know how it's not difficult) .. but rather somebody that really knows how.


Skills: Database Administration, Database Programming, MySQL, SQL

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About the Employer:
( 6 reviews ) Bangkok, Thailand

Project ID: #17161183

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Hi haha. Interesting. Considering your job description, my thought is the following... 1. you want to get the latest row for each data source , that includes several ratings. 2. so, you have to do group by operati More

$30 USD in 1 day
(6 Reviews)

15 freelancers are bidding on average $26 for this job

$29 USD in 1 day
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$25 USD in 1 day
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Hi there, I think I can solve it. Let's communicate to proceed further. I am professional and highly motivated, having over 6+ years of DBA and Development work experience in the software industry with MySQL an More

$30 USD in 1 day
(7 Reviews)

Hi, I would like to write the query to get sum of ratings across coin_id and data_item_id from different sources. Available to start now. Get in touch to discuss more. Regards, Manish

$30 USD in 1 day
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Hello , I'm Tamal, I have 6 years exp. I'm individual work on freelancer. So, I can finish it within short time. My portfolio is : [login to view URL] My Sample: E-Commerce Projects (Online Shopping) ------ More

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Dear Sir, After reading the job description I am confident that I would be a perfect fit for this position as my experience and abilities precisely match your requirements. Looking forward to hearing from you soon. T More

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hi give me the sampledb i will prepare the query and deliver to you . i could have good experience in writing quieries

$28 USD in 1 day
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Hi, I'm an experienced programmer and Linux systems administrator. Constructing a MySQL as per your request won't be a problem.

$29 USD in 1 day
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Hi, dear! I saw your proposal. I feel confidence about your project. I am a excellent web developer. I can perfectly do your job. If you give me chance, you have good result in short time. I hope you will hire m More

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Hello How are you I read your job description carefully I have many good experience in Mysql Query I can finish your job quickly and quickly If you hire me, I will do my best and make you satisfied Thanks!

$25 USD in 1 day
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Hello friend, I could help you with the requirement you have. I have the experience in SQL to solve the need you have. Thank you

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".....Select SUM([login to view URL]) From main_table AS m Left Join data_item AS d On m.data_item_id = [login to view URL] Order By [login to view URL] Desc ......" Dear sir I am a professional database developer. If you want I can do using teamv More

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Hi I think I understand what you are getting at. Please tell me if I am correct. Given say you have some data like the following coin_id, data_item_id, rating, created_at 1, 1, 5, '2018-6-13 10:15' 1, 2, 6, More

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