SQLServer2000MILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中UNION与UNION ALL的区别
UNION 运算符:
将两个或更多查询的结果组合为单个结果集,该结果集包含联合查询中的所有查询的全部行。这与使用联接组合两个表中的列不同。
使用 UNION 组合两个查询的结果集的两个基本规则是:
所有查询中的列数和列的顺序必须相同。
数据类型必须兼容。
这种多结果的查询组合为单一结果集在实际中应用的非常方便。但在应用中也有有着问题,如下实例可以进一步说明问题。
问题描述:
为了进一步分析与统计企业中关键部件的生产进度情况,采用了一个表Key_Item_Cal,其结构如图一:
图一
通过联合查询,将查询分为三个方面:
1、提出数据的基础明细,其代码如下:
SELECT dbo.Key_item.Key_item_name AS Item_Name,
dbo.H_MORVE.QTY_RECVD1 AS Quantity, dbo.Key_item.Style AS Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
WHERE (dbo.Key_item.Key_item <> 1)
Order by Style asc
其结果为:
2、提出数据的一级汇总明细,其代码如下:
SELECT dbo.Key_item.Key_item_name AS Item_Name,
SUM(dbo.H_MORVE.QTY_RECVD1) AS Quantity,MAX(dbo.Key_item.Style) AS Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
WHERE (dbo.Key_item.Key_item <> 1)
GROUP BY dbo.Key_item.Style,dbo.Key_item.Key_item_name
order by Style
其结果如图如示:
3、提出数据的二级汇总明细,其代码如下:
SELECT MAX(dbo.Key_item.Key_item_name) as Item_Name,
SUM(dbo.H_MORVE.QTY_RECVD1) as Quantity,
dbo.Key_item.Style as Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
GROUP BY dbo.Key_item.Style
ORDER BY dbo.Key_item.Style asc
其结果如图所示:
总体的设计就如以上所示,但通过UNION联接的时候出现了新的问题。通过以下例子,就可以看出UNION与UNION ALL的区别
方案一,其代码如下:
SELECT dbo.Key_item.Key_item_name AS Item_Name,
dbo.H_MORVE.QTY_RECVD1 AS Quantity, dbo.Key_item.Style AS Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
WHERE (dbo.Key_item.Key_item <> 1)
UNION (
SELECT dbo.Key_item.Key_item_name AS Item_Name,
SUM(dbo.H_MORVE.QTY_RECVD1) AS Quantity,MAX(dbo.Key_item.Style) AS Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
WHERE (dbo.Key_item.Key_item <> 1)
GROUP BY dbo.Key_item.Style,dbo.Key_item.Key_item_name
UNION
SELECT MAX(dbo.Key_item.Key_item_name) as Item_Name, SUM(dbo.H_MORVE.QTY_RECVD1) as Quantity,
dbo.Key_item.Style as Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
GROUP BY dbo.Key_item.Style)
ORDER BY dbo.Key_item.Style asc
GO
其结果如下:
问题:
通过以上结果,可以发现GR180.14.2.1后机架、PY165G.14.2.1B后机架和PY165K.14.2.1后机架的明细与其二级汇总值明显不符。而二级汇总的值是正确,为什么明细与汇总值不符?
针对这个问题,我采用了第二种方案。
方案二,其代码如下:
SELECT dbo.Key_item.Key_item_name AS Item_Name,
dbo.H_MORVE.QTY_RECVD1 AS Quantity, dbo.Key_item.Style AS Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
WHERE (dbo.Key_item.Key_item <> 1)
UNION ALL(
SELECT dbo.Key_item.Key_item_name AS Item_Name,
SUM(dbo.H_MORVE.QTY_RECVD1) AS Quantity,MAX(dbo.Key_item.Style) AS Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
WHERE (dbo.Key_item.Key_item <> 1)
GROUP BY dbo.Key_item.Style,dbo.Key_item.Key_item_name
UNION
SELECT MAX(dbo.Key_item.Key_item_name) as Item_Name,
SUM(dbo.H_MORVE.QTY_RECVD1) as Quantity,
dbo.Key_item.Style as Style
FROM dbo.Key_item LEFT OUTER JOIN
dbo.H_MORVE ON dbo.Key_item.Key_item = dbo.H_MORVE.ITEM
GROUP BY dbo.Key_item.Style)
ORDER BY dbo.Key_item.Style asc
GO
其结果如图:
通过以上的例子,大家可以看出在UNION与UNION ALL在应用上区别。
本人是应界本科生,愿从事企业信息信息化建设,希望有用人需求的企业与我联系。
伊妹儿:Leew4u@126.com
本人静候