Question

考虑下表：

sp100_id  _date        open  close  bullishness
-----------------------------------------------
1         2011-03-14   100   110    2.23
1         2011-03-15   115   100    1.00
1         2011-03-16   110   110    0.85
2         2011-03-14    90    85    0.99
2         2011-03-15    95    90    0.30
2         2011-03-16    92   100    4.66
3         2011-03-14   200   220    1.50
3         2011-03-15   250   210    1.75
3         2011-03-16   200   150    0.80

我想计算% return和bullishness之间每个股票的2011-03-14和2011-03-16，按% return DESC排名，并返回{{ 1}}，sp100_id和% return。我认为以下查询可以解决这个问题：

average bullishness

但是，它似乎总是只返回一行。然而，预期的产出是：

SELECT 
  sp100_id, 
  AVG(bullishness) as bullishness, 
  ((`close`-`open`) / `open`) as return_pct   
FROM
  stocks 
WHERE _date = BETWEEN '2011-03-14' AND '2011-03-16' 
ORDER BY return_pct DESC

我做错了什么？

Answer 1

您必须在查询中使用GROUP BY：

SELECT 
  sp100_id, 
  AVG(bullishness) as bullishness, 
  (((SELECT `close` FROM stocks s2
   WHERE s2.sp100_id=s1.sp100_id ORDER BY _date DESC LIMIT 1)
    -(SELECT `open` FROM stocks s3
   WHERE s3.sp100_id=s1.sp100_id ORDER BY _date ASC LIMIT 1)) / 
     (SELECT `open` FROM stocks s3
   WHERE s3.sp100_id=s1.sp100_id ORDER BY _date ASC LIMIT 1)) as return_pct
FROM
  stocks s1
WHERE _date BETWEEN '2011-03-14' AND '2011-03-16' 
GROUP BY sp100_id
ORDER BY return_pct DESC

如果没有GROUP BY，它只返回一个结果行，因为AVG将所有记录组合在一起。

我使用ORDER BY和LIMIT 1的子查询修复了return_pct的计算。

文档：GROUP BY (Aggregate) Functions

SQLfiddle

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