sql - MS ACCESS 2016 多重联接语法

Question

如何使用 MS ACCESS 2016 语法编写以下 SQL 查询？

SELECT 
    ticket.ticket_id,  
    a1.attr_val AS attr_val1,
    a2.attr_val AS attr_val2,
    a3.attr_val AS attr_val3
FROM ticket
    LEFT JOIN attr a1 ON ticket.ticket_id=a1.ticket_id AND a1.attr_type=1
    LEFT JOIN attr a2 ON ticket.ticket_id=a2.ticket_id AND a2.attr_type=2
    LEFT JOIN attr a3 ON ticket.ticket_id=a3.ticket_id AND a3.attr_type=3

预先感谢您的帮助!

Answer 1

MS Access 有这些 weird requirements about parentheses :

Join expression not supported. (Error 3296)

Possible causes:

• Your SQL statement contains multiple joins in which the results of the query can differ, depending on the order in which the joins are performed. You may want to create a separate query to perform the first join, and then include that query in your SQL statement.
• The ON statement in your JOIN operation is incomplete or contains too many tables. You may want to put your ON expression in a WHERE clause.

上述引用中建议的解决方案并不总是合适(例如，使用 WHERE 子句不是 LEFT JOIN 条件的选项)。

如何解决:

• 将连接放在括号中，这样每个连接表达式中只有一个连接；
• 用括号将 ON 表达式括起来；

SQL:

SELECT 
    ticket.ticket_id,  
    a1.attr_val AS attr_val1,
    a2.attr_val AS attr_val2,
    a3.attr_val AS attr_val3
FROM ((ticket
    LEFT JOIN attr AS a1 ON (ticket.ticket_id=a1.ticket_id AND a1.attr_type=1))
    LEFT JOIN attr AS a2 ON (ticket.ticket_id=a2.ticket_id AND a2.attr_type=2))
    LEFT JOIN attr AS a3 ON (ticket.ticket_id=a3.ticket_id AND a3.attr_type=3)