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POHow do I join the most recent row in one table to another table?
 

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  1. POHow do I join the most recent row in one table to another table?
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    <p>I have data that looks like this:</p> <pre><code>entities id name 1 Apple 2 Orange 3 Banana </code></pre> <p>Periodically, a process will run and give a score to each entity. The process generates the data and adds it to a scores table like so:</p> <pre><code>scores id entity_id score date_added 1 1 10 1/2/09 2 2 10 1/2/09 3 1 15 1/3/09 4 2 10 1/03/09 5 1 15 1/4/09 6 2 15 1/4/09 7 3 22 1/4/09 </code></pre> <p>I want to be able to select all of the entities along with the most recent recorded score for each resulting in some data like this:</p> <pre><code>entities id name score date_added 1 Apple 15 1/4/09 2 Orange 15 1/4/09 3 Banana 15 1/4/09 </code></pre> <p>I can get the data for a single entity using this query:</p> <pre><code>SELECT entities.*, scores.score, scores.date_added FROM entities INNER JOIN scores ON entities.id = scores.entity_id WHERE entities.id = ? ORDER BY scores.date_added DESC LIMIT 1 </code></pre> <p>But I'm at a loss for how to select the same for all entities. Perhaps it's staring me in the face?</p> <p>Thank you very kindly for taking the time.</p> <p>Thanks for the great responses. I'll give it a few days to see if a preferred solution bubbles up then I'll select the answer.</p> <p>UPDATE: I've tried out several of the proposed solutions, the main issue I'm facing now is that if an entity does not yet have a generated score they don't appear in the list. </p> <p>What would the SQL look like to ensure that all entities are returned, even if they don't have any score posted yet?</p> <p>UPDATE: Answer selected. Thanks everyone!</p>
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