mysql - 这个 SQl 是否被视为 JOIN？

Question

我正在使用 MySQl 根据“模块”表中的类别 ID 对 1 个表中的名称进行分类。

我有以下 SQL 可以很好地满足我的需求，但我想知道这是否被视为 JOIN ？

因为它没有调用JOIN？

SELECT  `mo_category_fk` ,  `mo_name_vc` ,  `mc_name_vc`
FROM x_modcats mc, x_modules m
WHERE mc.mc_id_pk = m.mo_category_fk
AND m.mo_folder_vc =  :module

Answer 1

是的 - 在 MySQL 中，隐式连接和显式连接具有相同的执行计划。您可以使用 EXPLAIN 来验证这一点。但这里是另一个线程的示例:

mysql> explain select * from table1 a inner join table2 b on a.pid = b.pid;
+----+-------------+-------+------+---------------+------+---------+--------------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref          | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+--------------+------+-------+
|  1 | SIMPLE      | b     | ALL  | PRIMARY       | NULL | NULL    | NULL         |  986 |       |
|  1 | SIMPLE      | a     | ref  | pid           | pid  | 4       | schema.b.pid |   70 |       |
+----+-------------+-------+------+---------------+------+---------+--------------+------+-------+
2 rows in set (0.02 sec)

mysql> explain select * from table1 a, table2 b where a.pid = b.pid;
+----+-------------+-------+------+---------------+------+---------+--------------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref          | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+--------------+------+-------+
|  1 | SIMPLE      | b     | ALL  | PRIMARY       | NULL | NULL    | NULL         |  986 |       |
|  1 | SIMPLE      | a     | ref  | pid           | pid  | 4       | schema.b.pid |   70 |       |
+----+-------------+-------+------+---------------+------+---------+--------------+------+-------+
2 rows in set (0.00 sec)