subquery: on clause is ambiguous - mysql

Question

SELECT *
FROM (
`lecture` AS l
)
LEFT JOIN `professor` AS p ON `p`.`professor_id` = `l`.`professor_id`
WHERE `lecture_sem` = '20141'
AND (
lecture_name LIKE '%KEYWORD%'
OR lecture_code LIKE '%KEYWORD%'
OR p.professor_name LIKE '%KEYWORD%'
)
AND (
SELECT COUNT( DISTINCT s1.yoil, s1.start_time, s1.end_time )
FROM schedule AS s1
INNER JOIN schedule AS s2 ON ( s1.lecture_id
IN (
SELECT lecture_id
FROM timeitem
WHERE timetable_id =890
)
AND s2.yoil = s1.yoil
AND (
(
s1.start_time <= s2.start_time
AND s2.end_time <= s1.end_time
) )
AND s2.lecture_id = lecture_id # <-- HERE
)
) >0
LIMIT 0 , 30
I want to use where column like this:
s2.lecture_id = lecture_id
or,
s2.lecture_id = l.lecture_id
So I want to use parent column in subquery, but error occurs:
Column 'lecture_id' in on clause is ambiguous
I googled many answers about this problem ("on clause is ambiguous"), they said I should replace this query to joining two queries. But I don't have a clue how to transform this query.

Answer 1

I believe the following does the equivalent query, but I haven't tested it.
The technique is to move the correlated subquery into the FROM clause as a derived table so that it gets run only once, producing a result for each lecture_id (hence the GROUP BY).
I also factored out the subquery for timetable, which I believe can be rewritten as a JOIN.
And I suspect the join to professor may be properly an INNER JOIN -- how can you have a lecture without a professor?
SELECT l.*, p.*
FROM lecture AS l
INNER JOIN professor AS p ON p.professor_id = l.professor_id
INNER JOIN (
SELECT s2.lecture_id, COUNT( DISTINCT s1.yoil, s1.start_time, s1.end_time ) AS count
FROM schedule AS s1
INNER JOIN schedule AS s2 ON s2.yoil = s1.yoil
AND s1.start_time <= s2.start_time AND s2.end_time <= s1.end_time
INNER JOIN timeitem AS t ON s1.lecture_id = t.lecture_id
WHERE t.timetable_id = 890
GROUP BY s2.lecture_id
) AS c ON l.lecture_id = c.lecture_id
WHERE l.lecture_sem = '20141'
AND c.count > 0
AND (
l.lecture_name LIKE '%KEYWORD%'
OR l.lecture_code LIKE '%KEYWORD%'
OR p.professor_name LIKE '%KEYWORD%'
)
LIMIT 0 , 30
Anyway, even if the query isn't perfect, it demonstrates how one would refactor it to avoid a correlated subquery.

Answer 2

The line you identified in your code isn't an ON clause.
Instead, I think the error is referring to the following section.
AND (
SELECT COUNT( DISTINCT s1.yoil, s1.start_time, s1.end_time )
FROM schedule AS s1
INNER JOIN schedule AS s2 ON ( s1.lecture_id
IN (
# vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
SELECT lecture_id # <---- HERE
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FROM timeitem
WHERE timetable_id =890
)
You can fix this by creating an alias for the timeitem table, and prefixing the column with this prefix:
IN (
SELECT ti.lecture_id
FROM timeitem as ti
WHERE ti.timetable_id =890
)
But as Bill Karwin pointed out in his answer, you have other logical issues that need to be addressed.