MySQL Nested SQL with limits - mysql

Question

I know it's not possible to use limits within nested INs, but I think there is a way to do this, I'm just not sure how.
I have a table that contains both ratings and comments (simplified for explanation)
mySingleTable:
+----+------------------+-----------+-----------+-----------------+
| id | reviewer_comment | is_rating | parent_id | reviewer_rating |
+----+------------------+-----------+-----------+-----------------+
| 1 | well done rateA | 1 | 0 | 5 Stars |
| 2 | commentAonRateA | 0 | 1 | |
| 3 | commentBonRateA | 0 | 1 | |
| 4 | commentConRateA | 0 | 1 | |
| 5 | commentDonRateA | 0 | 1 | |
| 6 | commentEonRateA | 0 | 1 | |
| 7 | commentFonRateA | 0 | 1 | |
| 8 | well done rateB | 1 | 0 | 4 Stars |
| 9 | well done rateC | 1 | 0 | 5 Stars |
| 11 | well done rateD | 1 | 0 | 3 Stars |
| 12 | well done rateE | 1 | 0 | 2 Stars |
| 13 | well done rateF | 1 | 0 | 5 Stars |
| 14 | well done rateG | 1 | 0 | 3 Stars |
| 15 | commentAonRateD | 0 | 11 | |
+----+------------------+-----------+-----------+-----------------+
So,
if is_rating = 1, its a rating.
if is_rating = 0, its a comment on the rating (its parent rating is where parent_id=id)
so this would look like:
well done rateA *****
commentAonRateA
commentBonRateA
commentConRateA
commentDonRateA
commentEonRateA
commentFonRateA
well done rateB ****
well done rateC *****
well done rateD ***
commentAonRateD
well done rateE **
well done rateF *****
well done rateG ***
What I want to do is select the newest five ratings, with the ASSOCIATED newest 5 comments, using only 1 query
So, some how join these two:
SELECT ratings.*
FROM mySingleTable as ratings
WHERE
is_rating = 1
ORDER BY timestamp DESC LIMIT 0, 5
SELECT comments.*
FROM mySingleTable as comments
Where
comments.parent_id = ratings.id
AND is_rating = 0
ORDER BY timestamp DESC LIMIT 0, 5
The 2nd query needs to somehow know about the ratings query

Answer 1

Please try this query which is now simplified and tested.
SELECT *
FROM
(SELECT *,
IF (group_id = #prev,
#n := #n + 1,
#n := 1 AND #prev := group_id) as position
FROM (
SELECT mySingleTable.*, group_id
FROM mySingleTable
INNER JOIN
(SELECT id AS group_id
FROM mySingleTable
WHERE is_rating = 1
ORDER BY timestamp DESC LIMIT 0, 5
) AS top5ratings
ON mySingleTable.id = group_id OR mySingleTable.parent_id = group_id
ORDER BY group_id DESC,
mySingleTable.parent_id ASC,
timestamp DESC) AS all_reviews
JOIN (SELECT #n := 0, #prev := 0) AS setup) AS reviews
WHERE reviews.position < 7
Keep in mind that SELECT * is bad practice. I used it to simplify reading.

Answer 2

TRY THIS QUERY
SELECT comments.*
FROM
(
SELECT ratings.id
FROM mySingleTable as ratings
WHERE
is_rating = 1
ORDER BY timestamp DESC LIMIT 0, 5 ) AS Top5
INNER JOIN mySingleTable AS comments ON comments.parent_id = Top5.id
WHERE comments.is_rating = 0
ORDER BY comments.timestamp DESC LIMIT 0, 5