Question

我正在使用下面的SQL查询来连接主表上的3个表

SELECT main.pricedrop, 
       t1.pid, 
       t2.pid, 
       t3.pid 
FROM   table_main AS main 
       LEFT JOIN table1 AS t1 
              ON main.pid = t1.pid 
       LEFT JOIN table2 AS t2
              ON main.pid = t2.pid 
       LEFT JOIN table3 AS t3 
              ON main.pid = t3.pid 
ORDER  BY main.pricedrop ASC 
LIMIT  5;

上面的查询给了我这个结果：

+-----------+---------+------+--------------+
| pricedrop | pid     | pid  | pid          |
+-----------+---------+------+--------------+
|      8.69 |    NULL | NULL | 665803977232 |
|      9.53 |    NULL | NULL |     82210815 |
|     11.11 | 1786429 | NULL |         NULL |
|     11.11 | 1786456 | NULL |         NULL |
|     13.91 |    NULL | NULL | 687074177857 |
+-----------+---------+------+--------------+

无论如何我可以得到这种格式的结果：

+-----------+--------------+
| pricedrop | pid          |
+-----------+--------------+
|      8.69 | 665803977232 |
|      9.53 | 82210815     |
|     11.11 | 1786429      |
|     11.11 | 1786456      |
|     13.91 | 687074177857 |
+-----------+--------------+

Answer 1

您需要使用COALESCE函数，该函数将返回第一个非空值，如：

customize.setLayout = function setLayout(text) { /* yada yada */ };

Mysql多个连接组将常用字段名称合并为一个

2 个答案: