请教一个SQL语句!

[shybrian]

用一条语句从一个表PATHWAY中选出 PATH_ID

分解开来就是

select PATH_ID from pathway where content = 'a'


select PATH_ID from pathway where content = 'b'


找出相同的所有PATH_ID。

[shybrian]

是这样的意思
表中有PATH_ID（不是主键） 和CONTENT两列

要求找出CONTENT = A 和 CONTENT = B 且PATH_ID相同的所有的PATH_ID

[shine333]

SELECT path_id
FROM pathway p1,
pathway p2
WHERE p1.path_id = p2.path_id
AND p1.content = 'a'
AND p2.content = 'a'

[shybrian]

$from_to_sql = "select PATH_ID from pathway p1,pathway p2
where p1.PATH_ID=p2.PATH_ID
and p1.CONTENT='".$content_get1."'
and p2.CONTENT='".$content_get2."';";

为什么我执行的时候还是有问题

Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\pwps\from_to.php on line 12
路径共有条
Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\pwps\from_to.php on line 14

[luoyoumou]

SELECT p1.path_id
  FROM pathway p1,
  pathway p2
 WHERE p1.path_id = p2.path_id
  AND p1.content = 'a'
  AND p2.content = 'b';

[ACMAIN_CHM]

select *
from pathway a inn join pathway b on a.PATH_ID=b.PATH_ID
where a.CONTENT = 'A' and b.CONTENT = 'B'

[iihero]

mysql> select t1.p from (select path_id p from pathway where content = 'a') t1, (select path_id p from pathway where content='b') t2 where t1.p = t2.p;
+------+
| p |
+------+
| 2 |
+------+
1 row in set (0.00 sec)

[yumenfeiyu945]

什么意思？把要求说清楚点