我已经读到Joins比子查询更有效，我的查询非常慢，并且使用很多子查询，因此我想改进它，但不知道如何做。

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-该查询的目标是为每个房屋（即每个aacode）生成一个文本形式的字符串，以表格[Marital][AgeCat][Relationship][AgeCat][Relationship][AgeCat]等形式描述房屋。因此，三人房屋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，但是包含在下面：

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;

有几项关键的事情需要改变。

1. 目前，我无法从Rel字段连接到Relatives表，因此我正在使用一种名为RAL的Switch函数，必须有一种更好的方法。
2. 为了简单起见，我只包含了Rel2和Rel3等，但是在实际代码中，它取决于Rel13！因此，性能问题更加严重。
3. 我想用联接替换这些子查询，但是当子查询查找同一表中的另一条记录时，我不确定如何执行此操作。
4. 我对此非常不了解，我知道一些SQL，但是对于我有限的知识来说，此问题的复杂性太大