sql - Access : Overflow Error with UNION but not with UNION ALL or Individual Queries

Question

为什么在使用 UNION 查询而不是 UNION ALL 时会出现溢出错误？ UNION 每一侧的查询本身都可以正常工作，并且每个查询所作用的表是相同的，即具有完全相同结构的实时数据表和存档数据表。

查询工作:

SELECT Format(CVDate([DateID] & " " & [TimeID]),"yyyy/mm/dd hh:nn:ss") & "-" & [RecNum] AS DateTimeRecNumID, 
    [QC Records].WONum, 
    [QC Records].InspName1, 
    [QC Records].QtyInsp, 
    Nz([008],0)+Nz([011],0)+Nz([012],0)+Nz([013],0)+Nz([014],0)+Nz([015],0)+Nz([016],0)+Nz([017],0)+Nz([018],0)+Nz([019],0)+Nz([020],0)+Nz([022],0)+Nz([023],0)+Nz([029],0)+Nz([035],0)+Nz([036],0)+Nz([037],0)+Nz([040],0)+Nz([041],0)+Nz([044],0)+Nz([045],0)+Nz([046],0)+Nz([047],0)+Nz([048],0)+Nz([050],0)+Nz([052],0)+Nz([055],0)+Nz([057],0)+Nz([059],0)+Nz([060],0)+Nz([062],0)+Nz([064],0)+Nz([066],0)+Nz([070],0)+Nz([072],0)+Nz([075],0)+Nz([077],0)+Nz([080],0)+Nz([081],0)+Nz([082],0)+Nz([083],0)+Nz([084],0)+Nz([085],0)+Nz([086],0)+Nz([088],0)+Nz([095],0)+Nz([096],0)+Nz([097],0)+Nz([111],0)+Nz([113],0)+Nz([115],0)+Nz([116],0)+Nz([117],0)+Nz([118],0)+Nz([119],0)+Nz([120],0)+Nz([121],0)+Nz([122],0)+Nz([123],0)+Nz([124],0)+Nz([125],0)+Nz([126],0)+Nz([127],0)+Nz([128],0)+Nz([129],0)+Nz([130],0)+Nz([130],0) AS SumFaults,
    1-([SumFaults]/[QtyInsp]) AS PassRate,
    [QC Records].ItemNum
FROM [QC Records]
WHERE ((([QC Records].ProdSrc)="Production"))
UNION ALL
SELECT Format(CVDate([DateID] & " " & [TimeID]),"yyyy/mm/dd hh:nn:ss") & "-" & [RecNum] AS DateTimeRecNumID,
    [QC Records (Archive)].WONum,
    [QC Records (Archive)].InspName1,
    [QC Records (Archive)].QtyInsp,
    Nz([008],0)+Nz([011],0)+Nz([012],0)+Nz([013],0)+Nz([014],0)+Nz([015],0)+Nz([016],0)+Nz([017],0)+Nz([018],0)+Nz([019],0)+Nz([020],0)+Nz([022],0)+Nz([023],0)+Nz([029],0)+Nz([035],0)+Nz([036],0)+Nz([037],0)+Nz([040],0)+Nz([041],0)+Nz([044],0)+Nz([045],0)+Nz([046],0)+Nz([047],0)+Nz([048],0)+Nz([050],0)+Nz([052],0)+Nz([055],0)+Nz([057],0)+Nz([059],0)+Nz([060],0)+Nz([062],0)+Nz([064],0)+Nz([066],0)+Nz([070],0)+Nz([072],0)+Nz([075],0)+Nz([077],0)+Nz([080],0)+Nz([081],0)+Nz([082],0)+Nz([083],0)+Nz([084],0)+Nz([085],0)+Nz([086],0)+Nz([088],0)+Nz([095],0)+Nz([096],0)+Nz([097],0)+Nz([111],0)+Nz([113],0)+Nz([115],0)+Nz([116],0)+Nz([117],0)+Nz([118],0)+Nz([119],0)+Nz([120],0)+Nz([121],0)+Nz([122],0)+Nz([123],0)+Nz([124],0)+Nz([125],0)+Nz([126],0)+Nz([127],0)+Nz([128],0)+Nz([129],0)+Nz([130],0)+Nz([130],0) AS SumFaults,
    1-([SumFaults]/[QtyInsp]) AS PassRate,
    [QC Records (Archive)].ItemNum
FROM [QC Records (Archive)]
WHERE ((([QC Records (Archive)].ProdSrc)="Production"));

不起作用(区别是 UNION 之后的“ALL”:

SELECT Format(CVDate([DateID] & " " & [TimeID]),"yyyy/mm/dd hh:nn:ss") & "-" & [RecNum] AS DateTimeRecNumID, 
    [QC Records].WONum, 
    [QC Records].InspName1, 
    [QC Records].QtyInsp, 
    Nz([008],0)+Nz([011],0)+Nz([012],0)+Nz([013],0)+Nz([014],0)+Nz([015],0)+Nz([016],0)+Nz([017],0)+Nz([018],0)+Nz([019],0)+Nz([020],0)+Nz([022],0)+Nz([023],0)+Nz([029],0)+Nz([035],0)+Nz([036],0)+Nz([037],0)+Nz([040],0)+Nz([041],0)+Nz([044],0)+Nz([045],0)+Nz([046],0)+Nz([047],0)+Nz([048],0)+Nz([050],0)+Nz([052],0)+Nz([055],0)+Nz([057],0)+Nz([059],0)+Nz([060],0)+Nz([062],0)+Nz([064],0)+Nz([066],0)+Nz([070],0)+Nz([072],0)+Nz([075],0)+Nz([077],0)+Nz([080],0)+Nz([081],0)+Nz([082],0)+Nz([083],0)+Nz([084],0)+Nz([085],0)+Nz([086],0)+Nz([088],0)+Nz([095],0)+Nz([096],0)+Nz([097],0)+Nz([111],0)+Nz([113],0)+Nz([115],0)+Nz([116],0)+Nz([117],0)+Nz([118],0)+Nz([119],0)+Nz([120],0)+Nz([121],0)+Nz([122],0)+Nz([123],0)+Nz([124],0)+Nz([125],0)+Nz([126],0)+Nz([127],0)+Nz([128],0)+Nz([129],0)+Nz([130],0)+Nz([130],0) AS SumFaults,
    1-([SumFaults]/[QtyInsp]) AS PassRate,
    [QC Records].ItemNum
FROM [QC Records]
WHERE ((([QC Records].ProdSrc)="Production"))
UNION  
SELECT Format(CVDate([DateID] & " " & [TimeID]),"yyyy/mm/dd hh:nn:ss") & "-" & [RecNum] AS DateTimeRecNumID,
    [QC Records (Archive)].WONum,
    [QC Records (Archive)].InspName1,
    [QC Records (Archive)].QtyInsp,
    Nz([008],0)+Nz([011],0)+Nz([012],0)+Nz([013],0)+Nz([014],0)+Nz([015],0)+Nz([016],0)+Nz([017],0)+Nz([018],0)+Nz([019],0)+Nz([020],0)+Nz([022],0)+Nz([023],0)+Nz([029],0)+Nz([035],0)+Nz([036],0)+Nz([037],0)+Nz([040],0)+Nz([041],0)+Nz([044],0)+Nz([045],0)+Nz([046],0)+Nz([047],0)+Nz([048],0)+Nz([050],0)+Nz([052],0)+Nz([055],0)+Nz([057],0)+Nz([059],0)+Nz([060],0)+Nz([062],0)+Nz([064],0)+Nz([066],0)+Nz([070],0)+Nz([072],0)+Nz([075],0)+Nz([077],0)+Nz([080],0)+Nz([081],0)+Nz([082],0)+Nz([083],0)+Nz([084],0)+Nz([085],0)+Nz([086],0)+Nz([088],0)+Nz([095],0)+Nz([096],0)+Nz([097],0)+Nz([111],0)+Nz([113],0)+Nz([115],0)+Nz([116],0)+Nz([117],0)+Nz([118],0)+Nz([119],0)+Nz([120],0)+Nz([121],0)+Nz([122],0)+Nz([123],0)+Nz([124],0)+Nz([125],0)+Nz([126],0)+Nz([127],0)+Nz([128],0)+Nz([129],0)+Nz([130],0)+Nz([130],0) AS SumFaults,
    1-([SumFaults]/[QtyInsp]) AS PassRate,
    [QC Records (Archive)].ItemNum
FROM [QC Records (Archive)]
WHERE ((([QC Records (Archive)].ProdSrc)="Production"));

错误是“溢出”

我还尝试对 UNION ALL 查询执行 SELECT DISTINCT 查询，它也给了我“溢出”错误...??

Answer 1

“为什么在使用 UNION 查询而不是 UNION ALL 时会出现溢出错误？”

您表示您知道 UNION 仅返回不同的行，而 UNION ALL 返回包括重复项在内的所有行。仅使用UNION，数据库引擎必须对初始工作集应用排序，以便它可以识别哪些是重复行并将其从最终结果集中消除。该排序操作给数据库引擎带来了显着的额外负担，这顺便解释了为什么 UNION ALL 总是比 UNION 更快，而且通常要快得多。

在您的情况下，各个SELECT语句已经给数据库引擎带来了不寻常的负担。我以前从未见过使用 Nz() 67 次并将所有这些值相加来派生一个计算字段的 Access 查询。数据库引擎必须对每个源表的每一行再次执行该工作。

Access 可以处理一个 SELECT 的工作负载。当您UNION ALL 其中两个时，它仍然可以应对。但是，当您强加 UNION 所需的排序要求时，Access 就会出现阻塞。

如果您的下一个问题是“我可以做什么？”，我会建议您首先查看源表。 SELECT 查询的复杂性是表设计的结果。如果无法进行更改，至少考虑是否可以运行 UPDATE 语句将源表中的 Null 替换为 0；这可能会减轻负担，使 UNION 更简单(即没有所有这些 Nz 调用)SELECT 查询成功。

作为最后的手段，请考虑将每个 SELECT 的结果集附加到临时表中:

INSERT INTO scratch_table
    (
        DateTimeRecNumID,
        WONum,
        InspName1,
        QtyInsp,
        SumFaults,
        PassRate,
        ItemNum
    )
SELECT ...

那么 Access 也许能够处理...

SELECT DISTINCT *
FROM scratch_table;