从两个表中选择其中只有 1 个来自 table_1 的唯一结果答案

【问题标题】：Select from two tables WHERE only 1 unique result from table_1从两个表中选择其中只有 1 个来自 table_1 的唯一结果
【发布时间】：2014-07-12 04:34:53
【问题描述】：

我一直在寻找，似乎无法弄清楚如何获得以下信息，任何帮助非常感谢！

鉴于这些表格：

表_1

+-----------+----------+-------+
| firstName | lastName |  zip  |
+-----------+----------+-------+
| John      | Doe      | 80210 |
| Barty     | Crouch   | 80598 |
| Mary      | Jane     | 80233 |
| John      | Doe      | 80210 |
+-----------+----------+-------+

表_2

+-----------+----------+-------+
| firstName | lastName |  zip  |
+-----------+----------+-------+
| John      | Doe      | 80210 |
| Barty     | Crouch   | 80598 |
| Max       | Payne    | 80233 |
+-----------+----------+-------+

如果 Table_1 中该记录只有一个结果，我该如何选择表之间的匹配记录？

这样的事情（作为查询应该做什么的例子写出来的结尾部分是我无法弄清楚的）

SELECT Table_1.firstName,
   Table_1.lastName,
   Table_1.zip,
   Table_2.firstName,
   Table_2.lastName,
    Table_2.zip
FROM Table_1, Table_2
WHERE Table_1.firstName = Table_2.firstName and Table_1.lastName = Table_2.lastName and Table_1.zip = Table_2.zip
and ONLY ONE RESULT First,Last,zip FROM TABLE_1

这只会返回 Barty Crouch 80598

【问题讨论】：

为什么返回多余的列而不是三个？

标签： mysql sql

【解决方案1】：

加入派生表，该表是 table_1 中只有 1 个组计数的行的分组列表。：

SELECT T2.FirstName, T2.LastName, T2.Zip
FROM TABLE_2 AS T2
JOIN (
SELECT T1.FirstName, T1.LastName, T1.Zip
FROM TABLE_1 AS T1
GROUP BY T1.FirstName, T1.LastName, T1.Zip
HAVING COUNT(*) = 1) AS T1
  ON T1.FirstName = T2.FirstName
 AND T1.LastName = T2.LastName
 AND T1.Zip = T2.Zip

【讨论】：

这工作谢谢！我花了一段时间才让它在非常大的数据集上运行（对于这些稍微复杂的大量数据的 sql 来说是新手）。 SELECT T2.FirstName, T2.LastName, T2.mZip5, T2.BSDID, T2.Email, T2.Homephone, T2.MobilePhone FROM vanmatch.bsd AS T2 JOIN EACH ( SELECT T1.FirstName, T1.LastName, T1.mZip5 FROM vanmatch.van AS T1 GROUP BY T1.FirstName, T1.LastName, T1.mZip5 HAVING COUNT(*) = 1) AS T1 ON T1.FirstName = T2.FirstName AND T1.LastName = T2.LastName AND T1.mZip5 = T2.mZip5

【解决方案2】：

许多可能的变体之一：

SELECT Table_1.firstName,
   Table_1.lastName,
   Table_1.zip
FROM Table_1, Table_2
WHERE Table_1.firstName = Table_2.firstName and Table_1.lastName = Table_2.lastName and Table_1.zip = Table_2.zip
group by table_1.firstname, table_1.lastname, table_1.zip
having count(*) = 1

【讨论】：