如何在mysql中将两列与连接表连接起来答案

【问题标题】：How to concatenate two columns with joined table in mysql如何在mysql中将两列与连接表连接起来
【发布时间】：2015-01-24 23:29:32
【问题描述】：

我有两个表issue_details 和payees，如下所示：

表格：issue_details

+----------+------------+----------+----------+
| check_no | issue_date | payee_id | lddap_no | 
+----------+------------+----------+----------+
|        0 | 2015-01-01 |          | 11101-15 | 
|        1 | 2015-01-24 |          | 11101-15 |
|    34561 | 2015-01-24 | 10       |          |
|    34562 | 2015-01-24 | 13       |          | 
+----------+------------+----------+----------+

表格：收款人

+----------+--------------------+
| payee_id | payee_name         | 
+----------+--------------------+
| 1        | John Smith         | 
| 10       | Chen Lou           | 
| 11       | Mark Dello         |
| 12       | ANTRECCO           | 
| 13       | Shay Ridz          | 
+----------+--------------------+

我执行此查询是为了连接两个表来描述我的issue_details 表中的收款人姓名。

SELECT      
    issue_details.issue_date AS date,
    issue_details.check_no AS check_no,
    payees.payee_name AS payee 
FROM
    issue_details
INNER JOIN 
    payees ON issue_details.payee_id = payees.payee_id

结果：

+----------+------------+----------+
| check_no | issue_date | payee    | 
+----------+------------+----------+
|    34561 | 2015-01-24 | Chen Lou |       
|    34562 | 2015-01-24 | Shay Ridz|       
+----------+------------+----------+

如果我这样做：

SELECT      
    issue_details.issue_date AS date,
    issue_details.check_no AS check_no,
    CONCAT(payees.payee_name, '', lddap_no) AS payee 
FROM
    issue_details
INNER JOIN 
    payees ON issue_details.payee_id = payees.payee_id

结果还是和上面一样。它不连接两列 payee_name（从表收款人加入）和lddap_no。

这就是我想要发生的事情：

+----------+------------+----------+
| check_no | issue_date | payee    |  
+----------+------------+----------+
|        0 | 2015-01-01 | 11101-15 |      
|        1 | 2015-01-24 | 11101-15 |     
|    34561 | 2015-01-24 | Chen Lou |
|    34562 | 2015-01-24 | Shay Ridz|     
+----------+------------+----------+

请在此处帮助我的查询。将不胜感激。谢谢

【问题讨论】：

您需要LEFT OUTER JOIN 和IFNULL() 或COALESCE() 将NULLs 转换为空字符串。
如何使用 IFNULL() ？请告诉我如何将其放入我的查询中。谢谢

标签： php mysql join

【解决方案1】：

只需将INNER JOIN 更改为LEFT JOIN

SELECT      issue_details.issue_date AS date,
            issue_details.check_no AS check_no,
            payees.payee_name AS payee 
FROM
            issue_details
            LEFT JOIN payees ON
            issue_details.payee_id = payees.payee_id

【讨论】：

【解决方案2】：

SELECT      id.issue_date AS date,
            id.check_no AS check_no,
            COALESCE( p.payee_name, id.lddap_no ) AS payee 
FROM        issue_details id
            LEFT  JOIN payees p ON
            id.payee_id = p.payee_id

见SQLFiddle Demo

【讨论】：