SQL 由于列名错误，查询无法正常工作，但该列存在

Question

我对以下查询有疑问：

SELECT *
FROM `pageindex`
    FULL JOIN `pages` ON `pageindex`.`url` = `pages`.`page`
WHERE `pageindex`.`url` IS NULL;

我也试过这个：

SELECT *
FROM pageindex
    FULL JOIN pages ON pageindex.url = pages.page
WHERE pageindex.url IS NULL;

我收到这个错误：

ERROR 1054 (42S22): Unknown column 'pageindex.url' in 'where clause'

但我不明白为什么当该列确实存在时，这里是 table:

中的列

+--------------+--------------+------+-----+---------+-------+
| Field        | Type         | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+-------+
| url          | varchar(255) | NO   | PRI | NULL    |       |
| title        | varchar(255) | YES  | MUL | NULL    |       |
| keywords     | text         | YES  |     | NULL    |       |
| description  | text         | YES  |     | NULL    |       |
| last_updated | date         | YES  |     | NULL    |       |
| heading      | varchar(255) | YES  |     | NULL    |       |
| textcontent  | text         | YES  |     | NULL    |       |
| htmlcontent  | text         | YES  |     | NULL    |       |
| audiencetype | varchar(255) | YES  |     | NULL    |       |
+--------------+--------------+------+-----+---------+-------+

希望你能帮上忙，

谢谢

Answer 1

因为 MySQL 不支持 FULL JOIN，您的查询解释如下：

SELECT *
  FROM `pageindex` AS full
  JOIN `pages` ON `pageindex`.`url` = `pages`.`page`
 WHERE `pageindex`.`url` IS NULL;

SQL 由于列名错误，查询无法正常工作，但该列存在

SQL Query not working due to column name error however column exists

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