数据透视表中的行未合并

Question

我创建了下表来说明正在发生的事情

create table weather (
    WDate varchar(10),
    ItemCode varchar(8),
    ItemValue int,
    ItemUnits varchar(8))

insert into Weather values 
    ('2020-02-10', 'MAXTEMP', 6, 'degC'),
    ('2020-02-10', 'MINTEMP', 2, 'degC'),
    ('2020-02-10', 'RAIN', 0, 'mm'),

    ('2020-02-11', 'MAXTEMP', 5, 'degC'),
    ('2020-02-11', 'RAIN', 20, 'mm'),
    ('2020-02-11', 'MINTEMP', 1, 'degC'),

    ('2020-02-12', 'RAIN', 5, 'mm'),
    ('2020-02-12', 'MAXTEMP', 8, 'degC'),
    ('2020-02-12', 'MINTEMP', 2, 'degC')

数据的顺序并不总是相同，因为它可能来自可能未进行时间同步的设备。当我运行以下查询时

SELECT
    [wdate] as 'Date',
    [MINTEMP] as 'Min Temp',
    [MAXTEMP] as 'Max Temp',
    [RAIN] as 'Rain'
FROM
(
    SELECT
        *
    FROM
        weather
) rawdata
PIVOT
(
    min(ItemValue)
    FOR ItemCode IN ([MINTEMP], [MAXTEMP], [RAIN])
) pitem
ORDER BY WDate

我明白了

WDate       Min Temp  Max Temp  Rain
2020-02-10  2         6         NULL
2020-02-10  NULL      NULL      0
2020-02-11  1         5         NULL
2020-02-11  NULL      NULL      20
2020-02-12  2         8         NULL
2020-02-12  NULL      NULL      5

我无法弄清楚为什么 Rain 数据没有与 Min 和 Max Temp 位于同一行。我期待

WDate       Min Temp  Max Temp  Rain
2020-02-10  2         6         0
2020-02-11  1         5         20
2020-02-12  2         8         5

Answer 1

您必须“馈送”具有最少列数的枢轴。请注意，子选择 rawdata 中缺少 ItemUnits

示例

SELECT
    [wdate] as 'Date',
    [MINTEMP] as 'Min Temp',
    [MAXTEMP] as 'Max Temp',
    [RAIN] as 'Rain'
FROM
(
    Select WDate
          ,ItemCode
          ,ItemValue 
      from Weather
) rawdata
PIVOT
(
    min(ItemValue)
    FOR ItemCode IN ([MINTEMP], [MAXTEMP], [RAIN])
) pitem
ORDER BY WDate

退货

Date        Min Temp    Max Temp    Rain
2020-02-10  2           6           0
2020-02-11  1           5           20
2020-02-12  2           8           5