如何限制连接查询？

Question

我正在尝试导出每个客户只有一个地址簿条目的客户列表。

SELECT c.customers_id, c.customers_firstname, c.customers_lastname, 
ab.address_book_id, ab.customers_id, ab.entry_company, ab.entry_firstname, ab.entry_lastname, ab.entry_street_address 
FROM customers c 
INNER JOIN address_book ab 
ON c.customers_id=ab.customers_id 
WHERE 1=1 
ORDER BY c.customers_id ASC 

我在做什么错？

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编辑：我有超过1个地址簿条目，因为有些客户有2个保存的地址。但我只需要一个出口。

Answer 1

创建一个表，只有像我已经做了以下

SELECT c.customers_id, c.customers_firstname, c.customers_lastname, 
ab.address_book_id, ab.customers_id, ab.entry_company, ab.entry_firstname,  ab.entry_lastname, ab.entry_street_address 
FROM customers c 
INNER JOIN address_book ab ON c.customers_id=ab.customers_id 
INNER JOIN 
(SELECT customers_id, MAX(address_book_id) AS AddressBookID 
    FROM address_book 
    GROUP BY customers_id) AS NewAddressBook ON c.customers_id = NewAddressBook.customers_id AND ab.address_book_id = NewAddressBook.AddressBookID 
ORDER BY c.customers_id ASC 

Answer 2

我认为这应该工作返回一个客户ID和一个address_book_id - 它返回的MIN（address_book_id）：

SELECT c.customers_id, c.customers_firstname, c.customers_lastname, 
    ab.address_book_id, ab.customers_id, ab.entry_company, ab.entry_firstname, ab.entry_lastname, ab.entry_street_address 
FROM customers c 
    INNER JOIN address_book ab 
     ON c.customers_id=ab.customers_id 
    INNER JOIN (
     SELECT MIN(address_book_id) min_address_book_id, customers_id 
     FROM address_book 
     GROUP BY customers_id 
    ) m ON ab.customers_id = m.customers_id AND 
     ab.address_book_id = m.min_address_book_id 
ORDER BY c.customers_id ASC 

Answer 3

在MySQL中，你可以做到以下几点：

SELECT c.customers_id, c.customers_firstname, c.customers_lastname, 
ab.address_book_id, ab.customers_id, ab.entry_company, ab.entry_firstname, ab.entry_lastname, ab.entry_street_address 
FROM customers c 
INNER JOIN address_book ab 
ON c.customers_id=ab.customers_id 
group by c.customers_id 
ORDER BY c.customers_id ASC 

这拉的个任意值为所有其他领域。对于customer的字段，这些值是正确的，因为它们在所有行上都是相同的。对于​​的字段，选择一个任意值。

理论上，这可以混合来自不同行的值。虽然这在实践中没有发生，但没有保证。因此，这是一种使用MySQL中的隐藏列功能来执行所需操作的方法。

Answer 4

UPDATE：

由于没关系你这address_book条目检索，这个查询将与最大address_book_id值取的：

SELECT c.customers_id, 
     c.customers_firstname, 
     c.customers_lastname, 
     ab.address_book_id, 
     ab.customers_id, 
     ab.entry_company, 
     ab.entry_firstname, 
     ab.entry_lastname, 
     ab.entry_street_address 
    FROM customers c LEFT JOIN 
     address_book ab ON c.customers_id=ab.customers_id AND 
     ab.address_book_id = (SELECT MAX(address_book_id) 
           FROM address_book 
          WHERE customers_id = c.customers_id) 
ORDER BY c.customers_id; 

在理论上可以有顾客没有关联的地址簿条目。 LEFT JOIN将允许你拉他们。如果您不想要这种行为，只需将LEFT JOIN更改为INNER JOIN即可。

这里工作sqlfiddle

原来的答案

这是我的第一个答案，它会在MySQL的，虽然它可以任意取不同值的行。请参阅@Gordon Linoff的答案中的解释。

SELECT c.customers_id, 
     c.customers_firstname, 
     c.customers_lastname, 
     MAX(ab.address_book_id), 
     MAX(ab.customers_id), 
     MAX(ab.entry_company), 
     MAX(ab.entry_firstname), 
     MAX(ab.entry_lastname), 
     MAX(ab.entry_street_address) 
FROM customers c INNER JOIN 
    address_book ON c.customers_id=ab.customers_id 
GROUP BY c.customers_id, c.customers_firstname, c.customers_lastname, 
ORDER BY c.customers_id