Question

这是漫长的一天，也许这是一个简单的问题，但无论如何我都被卡住了。

基本上我有两个类似的表Sales和Forecasts。我正在尝试创建一个视图，从两个表中选择行，并选择给定模型+月份+国家/地区的任何内容。如果两个表都包含数据，Sales具有优先级，这意味着应省略Forecast行。

为了简化查询我正在使用CTE。实际上两个表的模式是不同的，并且连接了许多表，Forecasts包含只显示最后一个的历史行。

我创建了一个简化的架构和数据来向您展示我正在尝试做的事情：

WITH Sales AS
(
    SELECT 
        ID, Model, Month, Country,
        Amount              = Count,
        [Forecast / Sales]  = 'Sales'
    FROM dbo.Sales
)
, Forecasts AS
(
    SELECT 
        ID, Model, Month, Country,
        Amount              = Count,
        [Forecast / Sales]  = 'Forecast'
    FROM dbo.Forecast
)
SELECT  ID = COALESCE(s.ID, fc.ID), 
        Model = COALESCE(s.Model, fc.Model), 
        Month = COALESCE(s.Month, fc.Month),
        Country = COALESCE(s.Country, fc.Country),
        Amount = COALESCE(s.Amount, fc.Amount),
        [Forecast / Sales] = COALESCE(s.[Forecast / Sales], fc.[Forecast / Sales])
FROM Sales s
FULL OUTER  JOIN Forecasts fc 
    ON s.Model = fc.Model
        AND s.Month = fc.Month
        AND s.Country = fc.Country
ORDER BY ID,Month,Country,Model

这是一个带有示例数据的sql-fiddle：http://sqlfiddle.com/#!3/9081b/9/2

结果：

ID  MODEL   MONTH   COUNTRY AMOUNT  FORECAST / SALES
1   ABC December, 01 2013 00:00:00+0000 Germany 777 Sales
2   ABC January, 01 2014 00:00:00+0000  Germany 999 Sales
3   ABC February, 01 2014 00:00:00+0000 Germany 900 Sales
3   ABC February, 01 2014 00:00:00+0000 Germany 900 Sales
4   ABC January, 01 2014 00:00:00+0000  UK  600 Forecast
4   ABC February, 01 2014 00:00:00+0000 UK  444 Sales
5   ABC March, 01 2014 00:00:00+0000    UK  500 Forecast

此查询根据ID和源（最后一列）返回重复项。

3   ABC February, 01 2014 00:00:00+0000 Germany 900 Sales
3   ABC February, 01 2014 00:00:00+0000 Germany 900 Sales

显然，Sales行被多个Forecast重复 - 该模型+月份+国家/地区组合的行。如果Sales + Sales行没有重复项，那么我如何只获得Forecast行？如果没有Forecast行，我如何获得Sales行？

Answer 1

您的查询问题不在于使用COALESCE，而在于使用JOIN。 Forecast表格中有2行具有Model, Month, Country的相同组合，ID 2和3的行：

╔════╦═══════╦═════════════════════════╦═════════╦═══════╗
║ ID ║ Model ║          Month          ║ Country ║ Count ║
╠════╬═══════╬═════════════════════════╬═════════╬═══════╣
║  2 ║ ABC   ║ 2014-02-01 00:00:00.000 ║ Germany ║  1100 ║
║  3 ║ ABC   ║ 2014-02-01 00:00:00.000 ║ Germany ║   900 ║
╚════╩═══════╩═════════════════════════╩═════════╩═══════╝

它们都与ID表中的行Sales 3连接：

╔════╦═══════╦═════════════════════════╦═════════╦═══════╗
║ ID ║ Model ║          Month          ║ Country ║ Count ║
╠════╬═══════╬═════════════════════════╬═════════╬═══════╣
║  3 ║ ABC   ║ 2014-02-01 00:00:00.000 ║ Germany ║   900 ║
╚════╩═══════╩═════════════════════════╩═════════╩═══════╝

由于您的查询正在使用COALESCE(s.ID, fc.ID)，因此您在结果中获得了2行ID 3

Answer 2

Lamak's answer 提供了结果中重复行的原因。这是一个解决方案：

WITH Sales AS
( ... )
, Forecasts AS
( ...)
, Combos AS                             -- get all distinct
(                                       -- model + month + country  
   SELECT Model, Month, Country         -- combinations
   FROM Sales                           -- from Sales
 UNION                                             -- this is UNION DISTINCT
   SELECT Model, Month, Country
   FROM Forecasts                       -- and Forecasts
)
SELECT  ID = COALESCE(s.ID, f.ID), 
        c.Model, 
        c.Month,
        c.Country,
        Amount = COALESCE(s.Amount, f.Amount),
        [Forecast / Sales] = COALESCE(s.[Forecast / Sales], 
                                      f.[Forecast / Sales])
FROM Combos c
  LEFT JOIN Sales s
    ON  s.Model = c.Model
    AND s.Month = c.Month
    AND s.Country = c.Country
  LEFT JOIN Forecasts f 
    ON  s.Model IS NULL           -- join Forecasts only if there is no Sales
    AND f.Model = c.Model
    AND f.Month = c.Month
    AND f.Country = c.Country
ORDER BY ID, Month, Country, Model ;

测试时间： SQL-Fiddle

Answer 3

您似乎只想返回整个Sales集，并使用Forecasts中未找到的Sales条目对其进行补充。为此，我可能只使用UNION ALL like this：

WITH Sales AS
(
  ...
)
, Forecasts AS
(
  ...
)

SELECT ID, Model, Month, Country, Amount, [Forecast / Sales]
FROM Sales

UNION ALL

SELECT ID, Model, Month, Country, Amount, [Forecast / Sales]
FROM Forecasts
WHERE NOT EXISTS
(
  SELECT Model, Month, Country
  INTERSECT
  SELECT Model, Month, Country
  FROM Sales
);

FULL OUTER使用COALESCE连接复制行

3 个答案: