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POSelecting first and last values in a group
 

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    <p>I have a MySql table consisting of daily stock quotes (open, high, low, close and volume) which I'm trying to convert into weekly data on the fly. So far, I have the following function, which works for the highs, lows, and volume:</p> <pre><code>SELECT MIN(_low), MAX(_high), AVG(_volume), CONCAT(YEAR(_date), "-", WEEK(_date)) AS myweek FROM mystockdata GROUP BY myweek ORDER BY _date; </code></pre> <p>I need to select the first instance of _open in the above query. So for example, if there was a holiday on Monday (in a particular week) and stock market opened on Tuesday, _open value should be selected from the Tuesday that's grouped into its week. Similarly, the close value should be the last _close from that week.</p> <p>Is it possible to select something like FIRST() and LAST() in MySql so that the above could be wrapped up within a single SELECT rather than using nested select queries?</p> <p>Here's my table's create statement to get an idea of the schema:</p> <pre><code>delimiter $$ CREATE TABLE `mystockdata` ( `id` int(11) NOT NULL AUTO_INCREMENT, `symbol_id` int(11) NOT NULL, `_open` decimal(11,2) NOT NULL, `_high` decimal(11,2) NOT NULL, `_low` decimal(11,2) NOT NULL, `_close` decimal(11,2) NOT NULL, `_volume` bigint(20) NOT NULL, `add_date` date NOT NULL, PRIMARY KEY (`id`), KEY `Symbol_Id` (`symbol_id`,`add_date`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8$$ </code></pre> <p>Update: There are no nulls, wherever there's a holiday/weekend, the table does not carry any record for that date.</p>
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    1. USZishan
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    1. COAs you know, `FIRST` and `LAST` as you described don't exist in MySQL. It may be possible with one query, but it depends on your table schema… Update your post.
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      1. USJason McCreary
    2. COThanks, Jason. Please see my edits above.
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