Question

我想显示数据库产品组的平均价格。因此，我希望随时间推回该产品组中所有产品的平均价格。

首先，我想知道该组有多少价格变动。此查询使用此查询成功返回所有日期...

SELECT DISTINCT(DATE(gbp.prdate)) as dte
FROM sku AS s
  INNER JOIN mt_price gbp ON s.id = gbp.
WHERE (gbp.prdate < NOW() - INTERVAL ? DAY) AND (s.grp = ?)`

然后我在php中使用foreach生成以下查询...

$i = 1;
$qry = "SELECT s.id AS sid, s.sku, s.title AS s_title,";
foreach ($dates as $date) {
  $qry .= "(SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE(?) ORDER BY prdate LIMIT 1) AS ?, ";
  $datearr[] = $date;
}
$qry = substr($qry, 0, -2) . " ";
$qry .= "FROM sku AS s
  WHERE (s.grp = ?)
  GROUP BY s.id
  ORDER BY s.id";
$results = $db->prepare($qry);
foreach($datearr as $darr) {
  $results->bindParam($i++,$darr->dte,PDO::PARAM_STR);
  $results->bindParam($i++,$darr->dte,PDO::PARAM_STR);
}

上面的一个例子给了我这个查询...

SELECT s.id AS sid, s.rid, s.sku, s.title AS s_title,
  (SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE('2015-01-08') ORDER BY prdate LIMIT 1) AS '2015-01-08',
  (SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE('2015-02-12') ORDER BY prdate LIMIT 1) AS '2015-02-12',
  (SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE('2015-01-26') ORDER BY prdate LIMIT 1) AS '2015-01-26',
  (SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE('2015-02-08') ORDER BY prdate LIMIT 1) AS '2015-02-08',
  (SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE('2015-01-30') ORDER BY prdate LIMIT 1) AS '2015-01-30',
  (SELECT price FROM price WHERE price.sid = s.id AND prdate <= DATE('2015-02-02') ORDER BY prdate LIMIT 1) AS '2015-02-02'

来自sku AS 在哪里（s.cat =＆＃39; TLPT01＆＃39;） GROUP BY s.id. ORDER BY s.id

当我按上述方式运行此查询时，我得到了我期望的结果，每个SKU只有一个价格（低至LIMIT）以及正确的价格。然后，当DATE更改时，它会正确显示SKU的价格。我也好！

所以，我想要的是获得所有这些结果的平均值。如果我在AVG前面使用s.id，我会获得SKU的平均值，这显然不是任何结果。我想要返回的所有SKU的平均价格（因此，GROUP BY应该只给我一行信息）。当我将GROUP BY放在子查询之前时，我只是得到一个错误。

Answer 1

你没有编码你所说的话; 每个日期的平均值。对子查询使用avg查询（简化）：

select date, avg(avg_price) from (
    select group_id, date, avg(price) avg_price
    from mytable
    group by group_id, date
) x
group by date

内部查询将为每个group_ id和date生成一个avg值，外部查询仅按日期平均那些group_id / date值。

Answer 2

尝试按如下方式创建子查询（SELECT AVG（price）FROM price WHERE price.sid = s.id AND prdate＆lt; = DATE（？）GROUP BY price.sid）

Answer 3

我发现将子查询移动到LEFT JOIN解决方案中。然后，我可以对这些JOIN返回的价格进行AVG。我仍然不知道为什么我不能只是AVG子查询，但这种方法（虽然不是超级快）...工作。

SELECT s.cat, s.id AS sid, s.rid, s.sku, s.title AS s_title, AVG(pr1.price)
FROM sku AS s
  LEFT JOIN (SELECT sid, price, prdate FROM price WHERE prdate <= DATE('2014-12-21') ) AS pr1 ON s.id = pr1.sid
  ... <more from foreach, add more AVG on top line> ...
WHERE (s.cat = 'TLPT01')
GROUP BY cat

MySQL：子查询的平均值（不在FROM / GROUP BY中）

3 个答案: