MySQL左连接不同于简单连接。MySQL LEFT JOIN提供该表额外字段在左侧。 如果使用LEFT JOIN,得到的所有记录的匹配方式相同, 在左边表中得到的每个记录不匹配也会有一个额外的记录。 从而确保(在本例子),每次作者信息都会列出: SELECT * from tutorials_tbl; +-------------+----------------+-----------------+-----------------+ | tutorial_id | tutorial_title | tutorial_author | submission_date | +-------------+----------------+-----------------+-----------------+ | | | +-------------+----------------+-----------------+-----------------+ mysql> SELECT * FROM tcount_tbl; +-----------------+----------------+ | tutorial_author | tutorial_count | +-----------------+----------------+ | | mahnaz | NULL | | Jen | NULL | | | | +-----------------+----------------+ mysql> SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count -> FROM tutorials_tbl a LEFT JOIN tcount_tbl b -> ON a.tutorial_author = b.tutorial_author; +-------------+-----------------+----------------+ | tutorial_id | tutorial_author | tutorial_count | +-------------+-----------------+----------------+ | | Abdul S | NULL | | +-------------+-----------------+----------------+ rows in set (0.02 sec)