查看同一个表中的另一条记录时将 SQL 子查询转换为联接 Access 2010

我读过联接比子查询更有效，我有一个查询非常慢并且使用大量子查询，因此我想改进它但不知道如何改进。

我有以下表格：

 People  \\this table stores lists of individual people with the following fields
 ( 
    ID, \\Primary Key
    aacode Text, \\represents a individual house
    PERSNO number, \\represent the number of the person in the house e.g. person number 1
    HRP number, \\the PERSNO of the Housing Reference Person (HRP) the "main" person in the house
    DVHsize number, \\the number of people in the house
    R01 number, \\the persons relationship to the person who is PERSNO=1
    R02 number, \\the persons relationship to the person who is PERSNO=2
    R03 number, \\the persons relationship to the person who is PERSNO=3
    AgeCat text, \\the age range of the person e.g. 30-44
    xMarSta number, \\representing the marital satus of the person
)
Relatives \\this table stores the possible R01 numbers and their text equivalents
(
    ID Primary Key, \\all possible R01 values
    Relationship text, \\meaning of the corisponding R01 values
)
xMarSta \\this table store the possible xMarSta values and their text equivalents
(
    ID Primary Key \\all possible xMarSta values
    Marital text, \\meaning of corresponding R01 values
)

查询是：

HsHld- 此查询的目标是为每个房屋（即每个 aacode）生成一个以以下形式描述房屋的文本字符串[Marital][AgeCat][Relationship][AgeCat][Relationship][AgeCat]等等。所以三人房子的输出可能看起来像Married(30-44)Spouse(30-44)Child(1-4)

我知道我当前的 HsHld 代码很糟糕，但它包含在下面：

SELECT People.ID, People.aacode, People.PERSNO, 
       People.HRP, People.DVHsize, xMarSta.Marital,
       [Marital] & " (" & [AgeCat] & ")" & [RAL2] & [RAge2] & 
       [RAL3] & [RAge3] & [RAL4] & [RAge4] & [RAL5] & [RAge5] & 
       [RAL6] & [RAge6] & [RAL7] & [RAge7] & [RAL8] & [RAge8] AS HsTyp,
       (SELECT Fam2.R01  FROM People  AS Fam2  WHERE Fam2.aacode = People.aacode 
        AND Fam2.PERSNO = 2) AS Rel2,
       (SELECT Fam3.R01  FROM People  AS Fam3  WHERE Fam3.aacode = People.aacode 
        AND Fam3.PERSNO = 3) AS Rel3,
       Switch([Rel2] Is Null,Null,[Rel2]=-9,'DNA',[Rel2]=-8,'NoAns',
              [Rel2]=1,'Spouse',[Rel2]=2,'Cohabitee',[Rel2]<7,'Child',
              [Rel2]<10,'Parent',[Rel2]<15,'Sibling',[Rel2]=15,'Grandchild',
              [Rel2]=16,'Grandparent',[Rel2]=17,'OtherRelative',
              [Rel2]=20,'CivilPartner',True,'Other') AS RAL2,
       Switch([Rel3] Is Null,Null,[Rel3]=-9,'DNA',[Rel3]=-8,'NoAns',
              [Rel3]=1,'Spouse',[Rel3]=2,'Cohabitee',[Rel3]<7,'Child',
              [Rel3]<10,'Parent',[Rel3]<15,'Sibling',[Rel3]=15,'Grandchild',
              [Rel3]=16,'Grandparent',[Rel3]=17,'OtherRelative',
              [Rel3]=20,'CivilPartner',True,'Other') AS RAL3,
       (Select FAge2.AgeCat FROM People AS FAge2 
               WHERE FAge2.aacode = People.aacode 
               AND FAge2.PERSNO = 2
       ) AS RAge2,
       (Select FAge3.AgeCat FROM People AS FAge3 
               WHERE FAge3.aacode = People.aacode AND FAge3.PERSNO = 3
       ) AS RAge3
FROM Relatives 
RIGHT JOIN (xMarSta RIGHT JOIN People ON xMarSta.ID=People.xMarSta) 
           ON Relatives.ID=People.R01
WHERE (((People.HRP)=[People.PERSNO]))
ORDER BY People.aacode;

有几个关键的事情需要改变。

1. 目前我无法从 Rel 字段连接到亲戚 表工作，所以我使用名为 RAL 的 Switch 函数，必须 是一个更好的方式。
2. 为了简单起见，我在帖子中只包含了 Rel2 和 Rel3 等，但在实际代码中它上升到 Rel13！所以性能问题就更严重了。
3. 我想用联接替换这些子查询，但作为子查询 查看同一张表中的另一条记录，我不确定如何去 对这个。
4. 我对此非常不了解，我懂一点 SQL，但是 这个问题的复杂性对于我有限的知识来说太复杂了

首先，您有一个关系情况，但您拥有的表结构是使用列来表示关系。这将为您提供表中的 R01、R02、R03 ... R13 列。不幸的是，您将无法显着改变性能，因为您的表结构是重复的非规范化而不是关系型的。这意味着您的查询将需要所有这些重复代码，正如您提到的重复 13 次。这也意味着您的 switch 函数可以用 join 替换，但又会重复 13 次。

现在回到您的查询，您的查询中有多个子选择，您需要在 FROM 子句的左联接上联接相关表，并在您的选择上使用新的相关别名。现在您将在下面的示例中看到，对于每个 R01、R02 字段，您将有一个 Fam2、Fam3 关系，您需要对您的案例执行此操作 13 次，并且对于每个字段，您需要链接到亲属表（如我确实调用了 Relat2、Relat3 等）。现在，如果您可以将数据库结构更改为规范化结构，则可以真正简化此查询并使用更简单的联接。

看看这个是否可以帮助您理解该过程：

SELECT People.ID, People.aacode, People.PERSNO,  
       People.HRP, People.DVHsize, xMarSta.Marital, 
       [Marital] & " (" & [People.AgeCat] & ")" & [RAL2] & [RAge2] &  
       [RAL3] & [RAge3] AS HsTyp, 
       Fam2.R01 AS Rel2,
       Fam3.R01 AS Rel3, 
       Relat2.Relationship as RAL2,
       Relat3.Relationship as RAL3,
       Fam2.AgeCat AS RAge2, 
       Fam3.AgeCat AS RAge3 
FROM (((((People
LEFT JOIN (People  AS Fam2) ON (Fam2.aacode = People.aacode  and Fam2.PERSNO = 2))
LEFT JOIN (Relatives as Relat2) on Relat2.Id = Fam2.R01)
LEFT JOIN (People as Fam3)   ON (Fam3.aacode = People.aacode  AND Fam3.PERSNO = 3))
LEFT JOIN (Relatives as Relat3) on Relat3.Id = Fam3.R01)
LEFT JOIN xMarSta ON xMarSta.ID=People.xMarSta)
WHERE (People.HRP=[People.PERSNO])
ORDER BY People.aacode;