Question

假设我在名为wx_data的表格中有以下数据（临时值对于此处列出的日期和城市不准确）

city,        wx_date,    avg_temp
Kansas City, 2012-11-01, 28 
Kansas City, 2012-11-02, 42
Kansas City, 2012-11-03, 86
Kansas City, 2012-11-04, 39
Kansas City, 2012-11-05, 27
Kansas City, 2012-11-06, 65
Kansas City, 2012-11-07, 62
Kansas City, 2012-11-08, 55
Kansas City, 2012-11-09, 95
Kansas City, 2012-11-10, 90
Kansas City, 2012-11-11, 29
Saint Louis, 2012-11-01, 88 
Saint Louis, 2012-11-02, 42
Saint Louis, 2012-11-03, 30
Saint Louis, 2012-11-04, 60
Saint Louis, 2012-11-05, 85
Saint Louis, 2012-11-06, 65
Saint Louis, 2012-11-07, 62
Saint Louis, 2012-11-08, 32
Saint Louis, 2012-11-09, 80
Saint Louis, 2012-11-10, 80
Saint Louis, 2012-11-11, 33

我有一个查询，它确定每个城市的最大值和最小值，并返回标记为低和高的行，具体取决于给定日期的温度是否落在最高或最低观测温度的15％之内（在数据集）。

select 
      temp.city, 
      wx_date, 
      avg_tmp, 
      if(avg_tmp >=.85*temp.High, "High", "Low") 
   from 
      wx_data 
         inner join (select city, 
                            Min(avg_tmp) as Low, 
                            Max(avg_tmp) as High 
                        from 
                           wx_data
                        where
                           wx_date between '2012-11-02' and '2013-12-01'
                        group by city) as temp 
           on wx_data.city=temp.city 
   where 
        avg_tmp >= .85 * temp.High 
     or avg_tmp <= 1.15 * temp.Low
   order by 
      city, 
      wx_date;

我想修改查询以便返回上面的结果，但它只返回状态从低变为高的行，反之亦然。因此，我不希望连续几天看到数据返回低或高状态。

我该怎么做？

为了澄清，现在我的查询返回以下数据：

 Kansas City    November, 01 2012   28  Low
 Kansas City    November, 03 2012   86  High
 Kansas City    November, 04 2012   29  Low
 Kansas City    November, 05 2012   27  Low
 Kansas City    November, 09 2012   95  High
 Kansas City    November, 10 2012   90  High
 Kansas City    November, 11 2012   29  Low
 Saint Louis    November, 01 2012   33  Low
 Saint Louis    November, 02 2012   88  High 
 Saint Louis    November, 03 2012   87  High
 Saint Louis    November, 05 2012   85  High
 Saint Louis    November, 08 2012   32  Low
 Saint Louis    November, 09 2012   80  High
 Saint Louis    November, 10 2012   80  High
 Saint Louis    November, 11 2012   33  Low

我只希望它返回按城市从高状态转换为低状态的行，以及反向Versa，因此如果我的查询正确，则应返回以下9行。

 Kansas City    November, 01 2012   28  Low
 Kansas City    November, 03 2012   86  High
 Kansas City    November, 04 2012   29  Low
 Kansas City    November, 09 2012   95  High
 Kansas City    November, 11 2012   29  Low
 Saint Louis    November, 02 2012   88  High 
 Saint Louis    November, 08 2012   32  Low
 Saint Louis    November, 09 2012   80  High
 Saint Louis    November, 11 2012   33  Low

有关数据和查询结果的示例，请参阅http://www.sqlfiddle.com/#!2/384fb/1。

Answer 1

核心查询不会更像这样 - 根据你的定义......？

SELECT city
     , MAX(avg_temp) max_temp
     , 0.85*MAX(avg_temp) max_threshold
     , MIN(avg_temp) min_temp
     , 1.15 * MIN(avg_temp) min_threshold
  FROM wx_data 
 GROUP 
    BY city ;
+-------------+----------+---------------+----------+---------------+
| city        | max_temp | max_threshold | min_temp | min_threshold |
+-------------+----------+---------------+----------+---------------+
| Kansas City |       95 |         80.75 |       27 |         31.05 |
| Saint Louis |       88 |         74.80 |       30 |         34.50 |
+-------------+----------+---------------+----------+---------------+

......等等......

SELECT x.*
     , CASE WHEN x.avg_temp BETWEEN y.min_temp AND y.min_threshold THEN 'Low'
            WHEN x.avg_temp BETWEEN y.max_threshold AND y.max_temp THEN 'High'
            ELSE ''
            END status
  FROM wx_data x 
  JOIN 
     ( SELECT city
            , MAX(avg_temp) max_temp
            , 0.85*MAX(avg_temp) max_threshold
            , MIN(avg_temp) min_temp
            , 1.15 * MIN(avg_temp) min_threshold
         FROM wx_data GROUP BY city 
      ) y
    ON y.city = x.city;

+-------------+------------+----------+--------+
| city        | wx_date    | avg_temp | status |
+-------------+------------+----------+--------+
| Kansas City | 2012-11-01 |       28 | Low    |
| Kansas City | 2012-11-02 |       42 |        |
| Kansas City | 2012-11-03 |       86 | High   |
| Kansas City | 2012-11-04 |       39 |        |
| Kansas City | 2012-11-05 |       27 | Low    |
| Kansas City | 2012-11-06 |       65 |        |
| Kansas City | 2012-11-07 |       62 |        |
| Kansas City | 2012-11-08 |       55 |        |
| Kansas City | 2012-11-09 |       95 | High   |
| Kansas City | 2012-11-10 |       90 | High   |
| Kansas City | 2012-11-11 |       29 | Low    |
| Saint Louis | 2012-11-01 |       88 | High   |
| Saint Louis | 2012-11-02 |       42 |        |
| Saint Louis | 2012-11-03 |       30 | Low    |
| Saint Louis | 2012-11-04 |       60 |        |
| Saint Louis | 2012-11-05 |       85 | High   |
| Saint Louis | 2012-11-06 |       65 |        |
| Saint Louis | 2012-11-07 |       62 |        |
| Saint Louis | 2012-11-08 |       32 | Low    |
| Saint Louis | 2012-11-09 |       80 | High   |
| Saint Louis | 2012-11-10 |       80 | High   |
| Saint Louis | 2012-11-11 |       33 | Low    |
+-------------+------------+----------+--------+

编辑： ......并进一步扩展这个想法（用sqlfiddle数据集进行比特）......

 SELECT a.city,a.wx_date,a.avg_tmp FROM
 (
 SELECT x.*
      , IF(@prev = CASE WHEN x.avg_tmp BETWEEN y.min_tmp AND y.min_threshold THEN 'Low'
             WHEN x.avg_tmp BETWEEN y.max_threshold AND y.max_tmp THEN 'High'
             ELSE ''
             END, @i := 0, @i:=1) flag
      , @prev := CASE WHEN x.avg_tmp BETWEEN y.min_tmp AND y.min_threshold THEN 'Low'
             WHEN x.avg_tmp BETWEEN y.max_threshold AND y.max_tmp THEN 'High'
             ELSE ''
             END status
   FROM wx_data x 
   JOIN 
      ( SELECT city
             , MAX(avg_tmp) max_tmp
             , 0.85*MAX(avg_tmp) max_threshold
             , MIN(avg_tmp) min_tmp
             , 1.15 * MIN(avg_tmp) min_threshold
          FROM wx_data GROUP BY city 
       ) y
     ON y.city = x.city
   JOIN (SELECT @i:=NULL,@prev:=NULL) vars
  ORDER 
     BY city,wx_date
     ) a
  WHERE flag = 1 AND status <> '';

http://www.sqlfiddle.com/#!2/384fb/12

Answer 2

假设您的查询正确，并且您只想显示高/低值更改的行：

select city, wx_date, avg_tmp, hi_lo
from (
    select temp.city, wx_date, avg_tmp, 
    if(avg_tmp >=.85*temp.High,"High","Low") hi_lo,
    @prevHiLo = (avg_tmp >=.85*temp.High and @prevCity = temp.city) same_as_prev,
    @prevHiLo := (avg_tmp >=.85*temp.High),
    @prevCity := temp.city
    from wx_data 
    inner join 
    (select city, Min(avg_tmp) as Low, Max(avg_tmp) as High from wx_data
    where (wx_date between '2012-11-02' and '2013-12-01') group by city) 
    as temp on wx_data.city=temp.city 
    where (avg_tmp >= .85*temp.High or avg_tmp <= 1.15*temp.Low)  
    order by city, wx_date
) t1 
where same_as_prev = 0
order by city, wx_date

http://www.sqlfiddle.com/#!2/b6f42/2

CITY    WX_DATE AVG_TMP HI_LO
Kansas City November, 03 2012 00:00:00+0000 86  High
Kansas City November, 04 2012 00:00:00+0000 29  Low
Kansas City November, 09 2012 00:00:00+0000 95  High
Kansas City November, 11 2012 00:00:00+0000 29  Low
Saint Louis November, 02 2012 00:00:00+0000 88  High
Saint Louis November, 08 2012 00:00:00+0000 32  Low
Saint Louis November, 09 2012 00:00:00+0000 80  High
Saint Louis November, 11 2012 00:00:00+0000 33  Low

mysql查询，满足条件时返回行

2 个答案: