Sub Query counting character strings in MySQL - mysql

Question

LEFT JOIN
(
SELECT user_id, review, COUNT(user_id) totalCount
FROM reviews
GROUP BY user_id
) b ON b.user_id= b.user_id
I am trying to fit WHERE LENGTH(review) > 100 in this somewhere but every I put it, it gives me problems.
The sub-query above counts all total reviews by user_id. I simply want to add one more qualification. Only count reviews greater than 100 length.
On a side note, I've seen the function CHAR_LENGTH -- not sure if that i what I need either.
EDIT:
Here is complete query working perfectly as expected for my needs:
static public $top_users = "
SELECT u.username, u.score,
(COALESCE(a.totalCount, 0) * 4) +
(COALESCE(b.totalCount, 0) * 5) +
(COALESCE(c.totalCount, 0) * 1) +
(COALESCE(d.totalCount, 0) * 2) +
(COALESCE(u.friend_points, 0)) AS totalScore
FROM users u
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM items
GROUP BY user_id
) a ON a.user_id= u.user_id
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM reviews
GROUP BY user_id
) b ON b.user_id= u.user_id
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM ratings
GROUP BY user_id
) c ON c.user_id = u.user_id
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM comments
GROUP BY user_id
) d ON d.user_id = u.user_id
ORDER BY totalScore DESC LIMIT 25;";

Answer 1

LENGTH() returns the length of the string measured in bytes. You probably want CHAR_LENGTH() as it will give you the actual characters.
SELECT user_id, review, COUNT(user_id) totalCount
FROM reviews
WHERE CHAR_LENGTH(review) > 100
GROUP BY user_id, review
You're also not using GROUP BY correctly.
See the documentation

Answer 2

The query that you want is:
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount,
sum(case when length(review) > 100 then 1 else 0 end
) as NumLongReviews
FROM reviews
GROUP BY user_id
) b ON b.user_id= b.user_id
This counts both the reviews and the "long" reviews. That count is done using a case statement nested in a sum() function.