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POPostgreSQL GROUP BY different from MySQL?
 

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  1. POPostgreSQL GROUP BY different from MySQL?
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    <p>I've been migrating some of my MySQL queries to PostgreSQL to use Heroku. Most of my queries work fine, but I keep having a similar recurring error when I use group by:</p> <blockquote> <p>ERROR: column "XYZ" must appear in the GROUP BY clause or be used in an aggregate function</p> </blockquote> <p>Could someone tell me what I'm doing wrong?</p> <p><br> MySQL which works 100%:</p> <pre class="lang-sql prettyprint-override"><code>SELECT `availables`.* FROM `availables` INNER JOIN `rooms` ON `rooms`.id = `availables`.room_id WHERE (rooms.hotel_id = 5056 AND availables.bookdate BETWEEN '2009-11-22' AND '2009-11-24') GROUP BY availables.bookdate ORDER BY availables.updated_at </code></pre> <p><br> PostgreSQL error:</p> <blockquote> <p>ActiveRecord::StatementInvalid: PGError: ERROR: column "availables.id" must appear in the GROUP BY clause or be used in an aggregate function:<br> SELECT "availables".* FROM "availables" INNER JOIN "rooms" ON "rooms".id = "availables".room_id WHERE (rooms.hotel_id = 5056 AND availables.bookdate BETWEEN E'2009-10-21' AND E'2009-10-23') GROUP BY availables.bookdate ORDER BY availables.updated_at</p> </blockquote> <p><br> Ruby code generating the SQL:</p> <pre class="lang-rb prettyprint-override"><code>expiration = Available.find(:all, :joins =&gt; [ :room ], :conditions =&gt; [ "rooms.hotel_id = ? AND availables.bookdate BETWEEN ? AND ?", hostel_id, date.to_s, (date+days-1).to_s ], :group =&gt; 'availables.bookdate', :order =&gt; 'availables.updated_at') </code></pre> <p><br> Expected Output (from working MySQL query):</p> <pre> +-----+-------+-------+------------+---------+---------------+---------------+ | id | price | spots | bookdate | room_id | created_at | updated_at | +-----+-------+-------+------------+---------+---------------+---------------+ | 414 | 38.0 | 1 | 2009-11-22 | 1762 | 2009-11-20... | 2009-11-20... | | 415 | 38.0 | 1 | 2009-11-23 | 1762 | 2009-11-20... | 2009-11-20... | | 416 | 38.0 | 2 | 2009-11-24 | 1762 | 2009-11-20... | 2009-11-20... | +-----+-------+-------+------------+---------+---------------+---------------+ 3 rows in set </pre>
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    1. COsooo... would I be better served using the distinct function on bookdate? If I did that, would I still need the group by clause?
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    2. CO`DISTINCT` is slower than `GROUP BY`. So you should be careful and prefer a `GROUP BY` solution if it is possible.
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