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POUsing COUNT on a self join query
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2013-05-29T21:06:48.163
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2013-05-31T19:30:46.540
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2013-05-31T19:30:46.540
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<p>I have a query that populates a double select list. The query retrieves main categories and sub categories from the same table via a self join. Basically it joins itself to get the subcategories in each category using id and parent id. I have tried to use COUNT to get the number of subcategories so I can add the number to the output of the first list. I didn't write the query , I just want to refactor it to count the subs in each main. </p> <pre><code>SELECT root.name AS root_name, root.link AS root_link, root.RETAIL AS root_RETAIL, root.WHOLESALE AS root_WHOLESALE, root.linkto AS root_linkto, root.keywords AS root_keywords, root.description AS root_description, root.id AS root_id, down1.name AS down1_name, down1.linkto AS down1_linkto, down1.link AS down1_link, down1.keywords AS down1_keywords, down1.description AS down1_description, down1.id AS down1_id, down1.parentid AS down1_parentid, down1.RETAIL AS down1_RETAIL, down1.WHOLESALE AS down1_WHOLESALE FROM categories AS root LEFT OUTER JOIN categories AS down1 ON down1.parentid = root.id WHERE root.parentid = 0 ORDER BY root_name, down1_name </code></pre> <p>This returns everything to populate both lists. I try to surround either <code>down1_name</code> or <code>down1_id</code> with <code>COUNT</code> but it counts everything - not the number of subs in each main. I'm not sure about using another self join to do it or a nested <code>SELECT</code> with <code>COUNT</code>. Any insight would be much appreciated. Tks.</p>
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<mysql>
Title
Using COUNT on a self join query
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