Question

I’m trying to execute the following SQL query in SQL Server 2008

String query = "SELECT SUM(r.rate),COUNT(q.best_answer_id) " +
                            "FROM questions_rating r,questions q " +
                            "WHERE r.question_id IN (SELECT question_id FROM questions WHERE user_id = 1) "+
                            "AND q.best_answer_id IN (SELECT answer_id FROM answers WHERE user_id = 1)";

These are the Tables

Questions_Rating

id---------question_id-----------user_id--------rate
1               1                    1            1
2               1                    2            1
3               1                    3           -1
4               2                    1           -1

The rate can only be either 1 or -1.

Questions

question_id------question-------user_id-------best_answer_id
1                   lala            1             3
2                   lala            2             5

Answers

answer_id---------answer--------user_id------question_id
1                   lala            4             1
2                   kaka            5             1
3                   dada            6             1
4                   fafa            7             2
5                   tata            8             2

The query is returning these results

SUM------COUNT
NULL       0

While it should return…

SUM------COUNT
1          0

Note that the following query returns the right result (1)

String query = "SELECT SUM(r.rate) " +
                            "FROM questions_rating r " +
                            "WHERE r.question_id IN (SELECT question_id FROM questions WHERE user_id = 1) ";

Answer 1

I think you should consider rewriting your query to use JOINS instead of your subqueries:

SELECT 
  SUM(r.rate) SumOfRate, 
  COUNT(a.answer_id) CountOfBest
FROM questions_rating r
INNER JOIN questions q
  ON r.question_id = q.question_id
  AND r.user_id = q.user_id
LEFT JOIN answers a
  ON q.best_answer_id = a.answer_id
  AND a.user_id = 1
WHERE r.user_id = 1

See SQL Fiddle with Demo

Returns the result:

| SUMOFRATE | COUNTOFBEST |
---------------------------
|         1 |           0 |