需要询问SQL Server中的关联查询

Question

我有2个查询，第一个：

SELECT XEDETALLES_BODEGA.IDPROD, SUM(XEDETALLES_BODEGA.CANTIDAD) AS CANTIDAD, MONTH (XEDETALLES_BODEGA.XFECHA) AS MES, 
       YEAR(XEDETALLES_BODEGA.XFECHA) AS ANO, CONVERT(DATETIME, CAST(YEAR(XEDETALLES_BODEGA.XFECHA) AS VARCHAR) + '-1-' + CAST(MONTH(XEDETALLES_BODEGA.XFECHA) AS VARCHAR) , 103)   AS FECHA
FROM XEDETALLES_BODEGA 
    LEFT OUTER JOIN xEGRESOS_BODEGA ON XEDETALLES_BODEGA.IDEGRESO = xEGRESOS_BODEGA.ID
WHERE (YEAR(XEDETALLES_BODEGA.XFECHA) = 2012) AND XEDETALLES_BODEGA.IDPROD <> 0
GROUP BY XEDETALLES_BODEGA.IDPROD, MONTH(XEDETALLES_BODEGA.XFECHA), YEAR(XEDETALLES_BODEGA.XFECHA)
ORDER BY XEDETALLES_BODEGA.IDPROD, MONTH(XEDETALLES_BODEGA.XFECHA), YEAR(XEDETALLES_BODEGA.XFECHA)

和第二个查询：

SELECT TOP (1) PRECIOUNIT
FROM XCDETALLES_BODEGA
WHERE (IDPROD = FIRSTQUERY.IDPROD) AND (XFECHA < FIRSTQUERY.FECHA)
ORDER BY XFECHA DESC

---

问题：对于第一个表上的每个记录，我需要在替换IDPROD和FECHA后获得第二个查询产生的PRECIOUNIT。

Answer 1

如果您希望第二个查询返回的列添加到第一个查询的结果，您可以简单地将第二个查询作为相关子查询结合到第一个查询中/ em>，像这样：

SELECT
  XEDETALLES_BODEGA.IDPROD,
  SUM(XEDETALLES_BODEGA.CANTIDAD) AS CANTIDAD,
  MONTH(XEDETALLES_BODEGA.XFECHA) AS MES, 
  YEAR(XEDETALLES_BODEGA.XFECHA) AS ANO,
  CONVERT(DATETIME, CAST(YEAR(XEDETALLES_BODEGA.XFECHA) AS VARCHAR) + '-1-' + CAST(MONTH(XEDETALLES_BODEGA.XFECHA) AS VARCHAR), 103) AS FECHA,
  (
    SELECT TOP (1) PRECIOUNIT
    FROM XCDETALLES_BODEGA
    WHERE (XCDETALLES_BODEGA.IDPROD = XEDETALLES_BODEGA.IDPROD)
      AND (XCDETALLES_BODEGA.XFECHA < CONVERT(DATETIME, CAST(YEAR(XEDETALLES_BODEGA.XFECHA) AS VARCHAR) + '-1-' + CAST(MONTH(XEDETALLES_BODEGA.XFECHA) AS VARCHAR), 103))
    ORDER BY XCDETALLES_BODEGA.XFECHA DESC
  ) AS PRECIOUNIT
FROM XEDETALLES_BODEGA 
  LEFT OUTER JOIN xEGRESOS_BODEGA ON XEDETALLES_BODEGA.IDEGRESO = xEGRESOS_BODEGA.ID
WHERE (YEAR(XEDETALLES_BODEGA.XFECHA) = 2012) AND XEDETALLES_BODEGA.IDPROD <> 0
GROUP BY XEDETALLES_BODEGA.IDPROD, MONTH(XEDETALLES_BODEGA.XFECHA), YEAR(XEDETALLES_BODEGA.XFECHA)
ORDER BY XEDETALLES_BODEGA.IDPROD, MONTH(XEDETALLES_BODEGA.XFECHA), YEAR(XEDETALLES_BODEGA.XFECHA)
;

但是，此查询还有改进的余地。

首先，我将介绍更短的表别名。请考虑重写：

SELECT
  xed.IDPROD,
  SUM(xed.CANTIDAD) AS CANTIDAD,
  MONTH(xed.XFECHA) AS MES, 
  YEAR(xed.XFECHA) AS ANO,
  CONVERT(DATETIME, CAST(YEAR(xed.XFECHA) AS VARCHAR) + '-1-' + CAST(MONTH(xed.XFECHA) AS VARCHAR), 103) AS FECHA,
  (
    SELECT TOP (1) PRECIOUNIT
    FROM XCDETALLES_BODEGA AS xcd
    WHERE (xcd.IDPROD = xed.IDPROD)
      AND (xcd.XFECHA < CONVERT(DATETIME, CAST(YEAR(xed.XFECHA) AS VARCHAR) + '-1-' + CAST(MONTH(xed.XFECHA) AS VARCHAR), 103))
    ORDER BY xcdXFECHA DESC
  ) AS PRECIOUNIT
FROM XEDETALLES_BODEGA AS xed
  LEFT OUTER JOIN xEGRESOS_BODEGA AS xeg ON xed.IDEGRESO = xeg.ID
WHERE (YEAR(xed.XFECHA) = 2012) AND xed.IDPROD <> 0
GROUP BY xed.IDPROD, MONTH(xed.XFECHA), YEAR(xed.XFECHA)
ORDER BY xed.IDPROD, MONTH(xed.XFECHA), YEAR(xed.XFECHA)
;

您是否同意较短的别名会使您的查询更具可读性？

另一个问题是您的分组标准，特别是这两项：

MONTH(xed.XFECHA), YEAR(xed.XFECHA)

他们当然会明确您的意图，但是当您将它们重新设置为datetime值时，它们也会进行多次转换。现在我们也在相关子查询中使用相同的datetime。这些转换绝对没有必要，因为你可以反过来谈论它。您可以将日期时间“舍入”到相应月份的开头，而不是从datetime中提取年份和月份，然后将其转换回datetime。以下表达式就是这样：

DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0)

现在，当您需要将月份和年份显示为数值时，您可以从上面的表达式中提取它们，因为这样可以提供相同的月份和年份。所以，现在看看你的查询：

SELECT
  xed.IDPROD,
  SUM(xed.CANTIDAD) AS CANTIDAD,
  MONTH(DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0)) AS MES, 
  YEAR(DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0)) AS ANO,
  DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0) AS FECHA,
  (
    SELECT TOP (1) PRECIOUNIT
    FROM XCDETALLES_BODEGA AS xcd
    WHERE (xcd.IDPROD = xed.IDPROD)
      AND (xcd.XFECHA < DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0))
    ORDER BY xcd.XFECHA DESC
  ) AS PRECIOUNIT
FROM XEDETALLES_BODEGA AS xed
  LEFT OUTER JOIN xEGRESOS_BODEGA AS xeg ON xed.IDEGRESO = xeg.ID
WHERE (YEAR(xed.XFECHA) = 2012) AND xed.IDPROD <> 0
GROUP BY xed.IDPROD, DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0)
ORDER BY xed.IDPROD, DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0)
;

我知道你在想什么。新表达式似乎使用了太多次，这不会使查询看起来非常干净，甚至更少，因为表达式不是那么短。这有帮助吗？是的，它可以。您可以使用派生表。将连接，WHERE过滤器和必要的列（包括计算月初的表达式）放入子选择中，让主查询从中提取数据。将分组，排序和相关子查询保留在主SELECT中。简而言之，这就是你可能最终得到的结果：

SELECT
  s.IDPROD,
  SUM(s.CANTIDAD) AS CANTIDAD,
  MONTH(s.XFECHA) AS MES, 
  YEAR(s.XFECHA) AS ANO,
  s.XFECHA,
  (
    SELECT TOP (1) PRECIOUNIT
    FROM XCDETALLES_BODEGA AS xcd
    WHERE (xcd.IDPROD = xed.IDPROD)
      AND (xcd.XFECHA < s.XFECHA
    ORDER BY xcd.XFECHA DESC
  ) AS PRECIOUNIT
FROM (
  SELECT
    xed.IDPROD,
    xed.CANTIDAD,
    DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0) AS FECHA
  FROM XEDETALLES_BODEGA AS xed
    LEFT OUTER JOIN xEGRESOS_BODEGA AS xeg ON xed.IDEGRESO = xeg.ID
  WHERE (YEAR(xed.XFECHA) = 2012) AND xed.IDPROD <> 0
) s
GROUP BY s.IDPROD, s.XFECHA
ORDER BY s.IDPROD, s.XFECHA
;

但是，如果您使用的是SQL Server 2005或更高版本，则不需要派生表 - 您可以使用CROSS APPLY。这里：

SELECT
  xed.IDPROD
  SUM(xed.CANTIDAD) AS CANTIDAD,
  MONTH(s.XFECHA) AS MES, 
  YEAR(s.XFECHA) AS ANO,
  s.XFECHA,
  (
    SELECT TOP (1) PRECIOUNIT
    FROM XCDETALLES_BODEGA AS xcd
    WHERE (xcd.IDPROD = xed.IDPROD)
      AND (xcd.XFECHA < s.XFECHA
    ORDER BY xcd.XFECHA DESC
  ) AS PRECIOUNIT
FROM XEDETALLES_BODEGA AS xed
  LEFT OUTER JOIN xEGRESOS_BODEGA AS xeg ON xed.IDEGRESO = xeg.ID
CROSS APPLY (
  SELECT DATEADD(MONTH, DATEDIFF(MONTH, 0, xed.XFECHA), 0) AS FECHA
) AS s
WHERE (YEAR(xed.XFECHA) = 2012) AND xed.IDPROD <> 0
GROUP BY xed.IDPROD, s.XFECHA
ORDER BY xed.IDPROD, s.XFECHA
;

Answer 2

您可以将第一个查询放入CTE并将其加入第二个查询。

;WITH 
 FIRSTQUERY (IDPROD, CANTIDAD, MES, ANO, FECHA)
 AS
 (
  SELECT XEDETALLES_BODEGA.IDPROD
    ,SUM(XEDETALLES_BODEGA.CANTIDAD) AS CANTIDAD
    ,MONTH(XEDETALLES_BODEGA.XFECHA) AS MES
    ,YEAR(XEDETALLES_BODEGA.XFECHA) AS ANO
    ,CONVERT(DATETIME, CAST(YEAR(XEDETALLES_BODEGA.XFECHA) AS VARCHAR) + '-1-' + CAST(MONTH(XEDETALLES_BODEGA.XFECHA) AS VARCHAR) , 103) AS FECHA
  FROM XEDETALLES_BODEGA 
  LEFT OUTER JOIN xEGRESOS_BODEGA ON XEDETALLES_BODEGA.IDEGRESO = xEGRESOS_BODEGA.ID
  WHERE (YEAR(XEDETALLES_BODEGA.XFECHA) = 2012) AND XEDETALLES_BODEGA.IDPROD <> 0
  GROUP BY XEDETALLES_BODEGA.IDPROD, MONTH(XEDETALLES_BODEGA.XFECHA),     YEAR(XEDETALLES_BODEGA.XFECHA)
  ORDER BY XEDETALLES_BODEGA.IDPROD, MONTH(XEDETALLES_BODEGA.XFECHA), YEAR(XEDETALLES_BODEGA.XFECHA)
 )
SELECT TOP (1) XCDETALLES_BODEGA.PRECIOUNIT
FROM XCDETALLES_BODEGA
LEFT JOIN FIRSTQUERY on FIRSTQUERY.IDPROD = XCDETALLES_BODEGA.IDPROD
WHERE XCDETALLES_BODEGA.XFECHA < FIRSTQUERY.FECHA
ORDER BY XFECHA DESC