MS Access 外部连接多个字段到单个记录

Question

我需要做与此处所示完全相同的事情：INNER or LEFT Joining Multiple Table Records Into A Single Row，但让它在 MS Access Query 中工作。

下面是场景：

---

电话桌

+----------------+-------------+
| Field          | Type        |
+----------------+-------------+
| f_id           | int(15)     |
| f_client_id    | int(11)     |
| f_phone_type   | varchar(50) |
| f_phone_number | varchar(13) |
+----------------+-------------+

客户表

+-----------------------------+--------------+------+-----+
| Field                       | Type         | Null | Key |
+-----------------------------+--------------+------+-----+
| f_id                        | int(15)      | NO   | PRI |
| f_first_name                | varchar(13)  | YES  | MUL |
| f_mi                        | char(1)      | YES  |     |
| f_last_name                 | varchar(20)  | NO   | MUL |
+-----------------------------+--------------+------+-----+

使用标准的 LEFT 或 INNER 连接，我会得到这样的结果：

+------------+------------+--------------+
| name       | Phone Type | Phone Number |
+------------+------------+--------------+
| John Smith | Home       | 712-555-6987 |
| John Smith | Work       | 712-555-1236 |
+------------+------------+--------------+

我需要一个查询，以提供属于给定客户的工作和家庭电话号码：

+------------+----------------+--------------+
| Name       | Work Number    | Home Number  |
+------------+----------------+--------------+
| John Smith | 712-555-1236   | 712-555-6987 |
+------------+----------------+--------------+

---

SQL 中的解决方案是

SELECT CONCAT(c.f_first_name, ' ', c.f_last_name) as Client_Name, 
       wp.f_phone_number as Work_Number,
       hp.f_phone_number as Home_Number

  FROM clients c
       LEFT OUTER JOIN phone hp
       ON hp.f_client_id = c.f_id
    AND
       hp.phone_type = 'home'
       LEFT OUTER JOIN phone wp
       ON wp.f_client_id = c.f_id
    AND
       wp.phone_type = 'work'

但这并不能转化为 MS Access，加入失败。通过 Access 完成相同任务的最佳方式是什么？

Answer 1

还有两个问题你还没有发现。

1. Access 或其数据库引擎中没有 CONCAT() 函数
2. 您的查询尝试使用 phone_type，但实际的字段名称是 f_phone_type

当连接两个以上的表时，Access 的数据库引擎需要括号。使用查询设计器设置连接是最简单的方法。查询设计器还将用 LEFT JOIN 替换 LEFT OUTER JOIN；在 Access 2003 中，任何一种方式都适用于我。

这个很容易在查询设计器中构建，但只为同时拥有家庭和工作号码的客户返回行。我以它为起点，然后调整了类似于您原来的 ON 子句。

SELECT
    c.f_first_name & " " & c.f_last_name AS [Name],
    wp.f_phone_number AS [Work Number],
    hp.f_phone_number AS [Home Number]
FROM
    (Clients AS c
    LEFT JOIN Phones AS hp
    ON c.f_id = hp.f_client_id)
    LEFT JOIN Phones AS wp
    ON c.f_id = wp.f_client_id
WHERE
    hp.f_phone_type='Home'
    AND wp.f_phone_type='Work';

将这些 WHERE 条件移动到 ON 表达式中，就像在您的 SQL Server 示例中一样，将返回所有客户端，无论您是否有任何电话号码为他们存档。然而，这种方法需要在 ON 表达式周围加上括号。并且这些 JOINS 无法在查询设计器中显示。

SELECT
    c.f_first_name & " " & c.f_last_name AS [Name],
    wp.f_phone_number AS [Work Number],
    hp.f_phone_number AS [Home Number]
FROM
    (Clients AS c
    LEFT JOIN Phones AS hp
    ON (c.f_id = hp.f_client_id AND hp.f_phone_type='Home'))
    LEFT JOIN Phones AS wp
    ON (c.f_id = wp.f_client_id AND wp.f_phone_type='Work');

更新：就我自己而言，我更喜欢用子查询来做这件事。

SELECT
    c.f_first_name & " " & c.f_last_name AS [Name],
    wp.f_phone_number AS [Work Number],
    hp.f_phone_number AS [Home Number]
FROM
    (Clients AS c
    LEFT JOIN [
        SELECT f_client_id, f_phone_number
        FROM Phones
        WHERE f_phone_type='Home'
    ]. AS hp
    ON c.f_id = hp.f_client_id)
    LEFT JOIN [
        SELECT f_client_id, f_phone_number
        FROM Phones
        WHERE f_phone_type='Work'
    ]. AS wp
    ON c.f_id = wp.f_client_id;

Answer 2

也可以使用子查询，如：

SELECT (firstname & " " & lastname ) AS fullname,
  (SELECT f_PhoneNumber FROM tblPhones 
   WHERE  f_clientID = clients.id AND f_PhoneType = "Home")
   AS HomeNumber,
  (SELECT f_PhoneNumber FROM tblPhones 
   WHERE  f_clientID = clients.id AND f_PhoneType = "Work")
   AS WorkNumber
FROM clients