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POMoving average in postgresql
 

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  1. POMoving average in postgresql
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    <p>I have the following table in my Postgresql 9.1 database:</p> <pre><code>select * from ro; date | shop_id | amount -----------+----------+-------- 2013-02-07 | 1001 | 3 2013-01-31 | 1001 | 2 2013-01-24 | 1001 | 1 2013-01-17 | 1001 | 5 2013-02-10 | 1001 | 10 2013-02-03 | 1001 | 4 2012-12-27 | 1001 | 6 2012-12-20 | 1001 | 8 2012-12-13 | 1001 | 4 2012-12-06 | 1001 | 3 2012-10-29 | 1001 | 3 </code></pre> <p>I am trying to get a moving average comparing data against last 3 Thursdays without including the current Thursday. Here's my query:</p> <pre><code>select date, shop_id, amount, extract(dow from date), avg(amount) OVER (PARTITION BY extract(dow from date) ORDER BY date DESC ROWS BETWEEN 0 PRECEDING AND 2 FOLLOWING) from ro where extract(dow from date) = 4 </code></pre> <p>This is the result given</p> <pre><code>date | shop_id | amount | date_part | avg -----------+----------+--------+-----------+-------------------- 2013-02-07 | 1001 | 3 | 4 | 2.0000000000000000 2013-01-31 | 1001 | 2 | 4 | 2.6666666666666667 2013-01-24 | 1001 | 1 | 4 | 4.0000000000000000 2013-01-17 | 1001 | 5 | 4 | 6.3333333333333333 2012-12-27 | 1001 | 6 | 4 | 6.0000000000000000 2012-12-20 | 1001 | 8 | 4 | 5.0000000000000000 2012-12-13 | 1001 | 4 | 4 | 3.5000000000000000 2012-12-06 | 1001 | 3 | 4 | 3.0000000000000000 </code></pre> <p>I expect</p> <pre><code>date | shop_id | amount | date_part | avg -----------+----------+--------+-----------+-------------------- 2013-02-07 | 1001 | 3 | 4 | 2.6666666666666667 2013-01-31 | 1001 | 2 | 4 | 4.0000000000000000 2013-01-24 | 1001 | 1 | 4 | 6.3333333333333333 2013-01-17 | 1001 | 5 | 4 | 6.0000000000000000 2012-12-27 | 1001 | 6 | 4 | 5.0000000000000000 2012-12-20 | 1001 | 8 | 4 | 2012-12-13 | 1001 | 4 | 4 | 2012-12-06 | 1001 | 3 | 4 | </code></pre>
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    1. USGlicious
    1. USGlicious
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    1. CO+1 good question - Pg version, sample data, expected results. Thanks! Converted to SQLFiddle here: http://sqlfiddle.com/#!1/18891/1
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      1. USCraig Ringer
    2. COBTW, "date" is a terrible column name, since it's the name of a data type. Avoid using it. If you must use it, always qualify it with the table alias and double quote it, as shown here: http://sqlfiddle.com/#!1/18891/4
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      1. USCraig Ringer
    3. COThanks Craig :) This is just a sample dataset from a very large table. I just like to get the query right first.
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      1. USGlicious
 

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