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POHow to find out which rows match without having multiple results per row?
 

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  1. POHow to find out which rows match without having multiple results per row?
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    <p>In SQLite I have a table that is created like this (simplified):</p> <pre><code>CREATE TABLE [entries] ( [id] INTEGER NOT NULL PRIMARY KEY, [local] VARCHAR, [remote] VARCHAR, [value] INTEGER ); INSERT INTO entries (local, remote, value) VALUES ("a", "b", 1); INSERT INTO entries (local, remote, value) VALUES ("b", "a", -1); INSERT INTO entries (local, remote, value) VALUES ("b", "a", -1); INSERT INTO entries (local, remote, value) VALUES ("a", "d", 2); INSERT INTO entries (local, remote, value) VALUES ("a", "d", 2); INSERT INTO entries (local, remote, value) VALUES ("d", "a", -2); </code></pre> <p>Now I want to list combinations that match each other. Consider column <strong>local</strong> as local bank account and <strong>remote</strong> as remote bank account. Whenever a transaction is made from <strong>local</strong> to <strong>remote</strong> with value <strong>x</strong> and there exists a matching transaction which received the value <strong>x</strong> but as negative value (in relation to the first found), I want to have an output from SQLite.</p> <p>My current approach is like this:</p> <pre><code>sqlite3 -header demo.db \ "SELECT * FROM (SELECT * FROM entries) AS q1, (SELECT * FROM entries) AS q2 WHERE q1.local = q2.remote AND q1.remote = q2.local AND q1.value = (q2.value * -1)" </code></pre> <p>But this returns:</p> <pre><code>id|local|remote|value|id|local|remote|value 1|a|b|1|2|b|a|-1 1|a|b|1|3|b|a|-1 2|b|a|-1|1|a|b|1 3|b|a|-1|1|a|b|1 4|a|d|2|6|d|a|-2 5|a|d|2|6|d|a|-2 6|d|a|-2|4|a|d|2 6|d|a|-2|5|a|d|2 </code></pre> <p>What I wanted as result would be this:</p> <pre><code>id|local|remote|value|id|local|remote|value 1|a|b|1|2|b|a|-1 4|a|d|2|6|d|a|-2 </code></pre> <p>Lines which don't have a matching partner should not be displayed - every line could only match to at most one other transaction. I tried with <strong>GROUP BY</strong>, but this didn't work with <strong>q1.id</strong> and <strong>q2.id</strong> as parameter.</p>
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      1. POHow to find out which rows match without having multiple results per row?
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    1. COWell, how do you decide which row to use when two rows are identical except for their ids?
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    2. COThe first result is ok, later there will be an extra check by date (+/- 3 days), but even there the first one will be sufficient.
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    3. COThis seems overly complicated for no reason. Can't you just add a column like `origin_id`, so you'll know exactly which one was the originating id? This would take a lot of guesswork out of the queries and make them a lot simpler.
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