SQL - MATCH AGAINST with HAVING and COUNT()

Question

does someone knows why this first query works and this second not?

first query (works):

SELECT *, 
       MATCH(username) AGAINST ('ergergergergergerg' IN BOOLEAN MODE) AS _score
FROM (ci_users) HAVING _score > '0';

second query (not working):

SELECT COUNT(id), 
       MATCH(username) AGAINST ('ergergergergergerg' IN BOOLEAN MODE) AS _score 
FROM (ci_users) HAVING _score > '0';

the first query returns exactly 24 rows, the second query returns 0 rows, while i just changed * to COUNT(id)

Answer 1

The first one return every row that matches.

The second one contains an aggregation on id.

When aggregating, MySQL is smart enough (or should I say, stupid enough) to implicitly pick a any value from all fields that are queried, but not aggregated. So since you don't group by score and you don't aggregate score, MySQL will just return any of the scores of all records, of the intermediate result (before applying the having clause) including those that have a value of 0. So, this intermediate result may very well contain just a count of, say, 900 and a _score of 0. After filtering using having, no records remain.

Now, I would be happy to do a suggestion, but I cannot tell what you would actually want to be returned from that query.

SELECT COUNT(id)
FROM
  (SELECT 
    id,
    MATCH(username) AGAINST ('ergergergergergerg' IN BOOLEAN MODE) AS _score 
  FROM (ci_users) HAVING _score > '0') x;

Or even better:

SELECT COUNT(id)
FROM (ci_users) 
WHERE MATCH(username) AGAINST ('ergergergergergerg' IN BOOLEAN MODE) > '0'