Two Limit Clauses in one statement? - mysql

Question

I am trying to build a product review page where users can comment any submitted reviews like Amazon. I want the page to display 3 user reviews as well as 2 responses to each of the reviews if they exist.
Here's the table
CREATE TABLE product_review
(`ID` int, `username` varchar(21), `review_title` varchar(30), `review_or_reply` int)
;
INSERT INTO product_review
(`ID`, `username`, `review_title`, `review_or_reply`)
VALUES
(1, 'Tom', 'Rip-off', 0),
(2, 'Peter', 'Rip-off', 1),
(3, 'May', 'Rip-off', 1),
(4, 'June', 'Rip-off', 1),
(5, 'Tommy', 'Worth the Price', 0),
(6, 'Sammy', 'Worth the Price', 1),
(7, 'Sam', 'Worth the Price',1),
(8, 'Bryan','Worth the Price',1),
(9, 'Sally', 'Average Product', 0)
;
The review_or_reply field is effectively a Yes or No field, where 0 means it's a review and 1 is the review's comments by other users.
Is there a single select statement that can limit 3 reviews and bring up two of their comments? For example:
Select `username`,`review_title`,`reply` from product_review where review_or_reply ='0' Limit 3
Select `username`,`review_title`,`reply` from product_review where review_or_reply = '1' and title = 'Rip-off' Limit 2
Select `username`,`review_title`,`reply` from product_review where review_or_reply = '1' and title = 'Worth the Price' Limit 2
Select `username`,`review_title`,`reply` from product_review where review_or_reply = '1' and title = 'Average Product' Limit 2
I want the output to be like this:
username review_title review_or_reply
Tom Rip-off 0
Peter Rip-off 1
May Rip-off 1
Tommy Worth the Price 0
Sammy Worth the Price 1
Sam Worth the Price 1
Sally Average Product 0

Answer 1

this will return 3 review_titles and then pull out two responses to that
SELECT
pr.*,
IF( #A = t.review_title,
IF(#B = 3, #B := 1, #B := #B +1)
, #B
) AS group_col,
#A := t.review_title
FROM (
SELECT
id,
username,
review_title
FROM product_review
WHERE reply ='0' LIMIT 3
) t
JOIN product_review pr ON pr.review_title=t.review_title
CROSS JOIN (SELECT #A := "", #B := 1) AS temp
GROUP BY group_col, review_title
ORDER BY id;
EDIT:
if there are more than one reply that is 0 in the database like so then this query will check for that. (since you did specify in the other queries that the reply had to be 1).
INSERT INTO product_review
(`ID`, `username`, `review_title`, `reply`)
VALUES
(1, 'Tom', 'Rip-off', 0),
(2, 'Peter', 'Rip-off', 1),
(3, 'May', 'Rip-off', 0),
(4, 'June', 'Rip-off', 1),
(5, 'Tommy', 'Worth the Price', 0),
(6, 'Sammy', 'Worth the Price', 1),
(7, 'Sam', 'Worth the Price',1),
(8, 'Bryan','Worth the Price',1),
(9, 'Sally', 'Average Product', 0),
(10, 'Timothy', 'Rip-off', 1)
notice that at id 3 there is a reply of 0 with id 10 a reply of 1. this query will correctly skip the reply = 0.
SELECT
pr.*,
IF( #A = t.review_title,
IF(pr.reply = 0, 1,
IF(#B = 3, #B := 1, #B := #B +1)
), #B
) AS group_col,
#A := t.review_title
FROM (
SELECT
DISTINCT
id,
username,
review_title
FROM product_review
WHERE reply ='0'
GROUP BY review_title
LIMIT 3
) t
JOIN product_review pr ON pr.review_title=t.review_title
CROSS JOIN (SELECT #A := "", #B := 1) AS temp
GROUP BY group_col, review_title
ORDER BY id;
DEMO

Answer 2

...or slower but simpler...
SELECT x.*
FROM product_review x
JOIN product_review y
ON y.review_title = x.review_title
AND y.id <= x.id
GROUP
BY x.id
HAVING COUNT(*) <= 3
ORDER
BY MIN(y.id)
LIMIT 3;