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POHow do I (SELECT) populate two objects from two tables with a single query?
 

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  1. POHow do I (SELECT) populate two objects from two tables with a single query?
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    <p>This should be something encountered by programmers often, but I never tried to get things this way.</p> <p>That is, I'll explain. Say, I need to fetch values from table Zoo like this: </p> <pre><code> @"SELECT z.predator, z.prey FROM Zoo AS z WHERE z.preyType=@carnivore" </code></pre> <p>Now I can get all the values to a List. I need to display the details of that querying in a grid. Now having got z.predator and z.prey values (which are for time sake integers, ie, their respective ids), I need to populate its meaningful values for displaying it to end user (I can't just display their ids). So now I might do something like this:</p> <pre><code> foreach (Zoo z in lstZoo) { Animal predator = GetFromAnimalTable(z.Predator) Animal prey = GetFromAnimalTable(z.Prey) } </code></pre> <p>This can make the program slower. Can I query all the details in one go? Something like this:</p> <pre><code> SELECT (SELECT * FROM ANIMAL WHERE id=z.predator), (SELECT * FROM ANIMAL WHERE id=z.prey) FROM Zoo AS z WHERE z.preyType=@carnivore </code></pre> <p>Provided I can read the values to a new bigger object? Or is this considered a bad practice?</p> <p><strong>UPDATE:</strong> Is it a standard practice to do this? Or is it recommended to individually populate as I stated first?</p> <p><strong>UPDATE 2</strong>: I seem to have made a terrible mistake of not posting the query exactly as I needed. I thought I could tweak the answers from here to meet my requirement, alas no with the parenthesis construction of Access queries.</p> <p>Here is how my actual query would be: </p> <pre><code>SELECT z.predator, p.lifeSpan, z.prey FROM Zoo AS z INNER JOIN Plants AS p ON p.parent_id=z.id WHERE z.preyType=@carnivore </code></pre> <p>Actually I had an INNER JOIN query already with another table. Now I need to get (SELECT) values of z.predator (and its corresponding values from Animals table), p.lifeSpan, z.prey (and its corresponding values from Animal table) meeting the INNER JOIN and WHERE condition.</p> <p>A pseudo code would look like this: </p> <pre><code>SELECT (SELECT * FROM ANIMAL WHERE id=z.predator), p.lifeSpan, (SELECT * FROM ANIMAL WHERE id=z.prey) FROM Zoo AS z INNER JOIN Plants AS p ON p.parent_id=z.id WHERE z.preyType=@carnivore </code></pre> <p>It should be pretty easy to extend my requirement from the answers here, but no success till now. I tried:</p> <pre><code>SELECT a1.*, p.lifeSpan, a2.* FROM Zoo AS z INNER JOIN Plants AS p ON p.parent_id=z.id INNER JOIN Animal AS a1 ON (a1.id=z.predator) INNER JOIN Animal AS a2 ON (a2.id=z.prey) WHERE z.preyType=@carnivore </code></pre> <p>And many variants of this with and without brackets. How can the above query be properly structured?</p>
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