Multiple Count() in Database - mysql

Question

I'm making a survey-applican with winforms and VB. This is the SQL I got so far to show statistics:
SELECT
tblAlt.altText,
Count(tblAnswers.answerID)
FROM tblAlt
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questionID = " & CInt(questionID) & "
GROUP BY tblAlt.altText;
This returns each alternatives for a question, and how many answered them. Is there a way I can count how many answered in total with the same SQL-query?
Tables involved are:
_______________ _______________ ___________ _______________
|_tblUsers____| |_tblAnswers___| |_tblAlt__| |_tblQuestion_|
| userID | | answerAltID | | altID | | questID |
| username | | userID | | altText | | questText |
|_____________| |______________| |_questID_| |_____________|
Any help would be appreciated!
This is what I used in the end:
SELECT
tblAlt.altText,
Count(tblAnswers.answerID),
(SELECT COUNT(answerID) FROM tblAnswers, tblAlt
WHERE tblAnswers.answerAltID = tblAlt.altID
AND tblAlt.questID = " & CInt(questionID) & ") as total_count
FROM tblAlt
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questID = " & CInt(questionID) & "
GROUP BY tblAlt.altText;

Answer 1

Use ROLLUP:
SELECT
tblAlt.altText,
Count(tblAnswers.answerID)
FROM tblAlt
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questionID = " & CInt(questionID) & "
GROUP BY tblAlt.altText WITH ROLLUP;
If you want one-time computation(to make query efficient), use CROSS JOIN. Don't worry, this CROSS JOIN won't yield cartesian product, it's only one row. This might be faster than subquery approach:
SELECT
tblAlt.altText,
Count(tblAnswers.answerID), x.total_count
FROM tblAlt
cross join (SELECT COUNT(answerID) as total_count FROM tblAnswers) as x
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questionID = " & CInt(questionID) & "
GROUP BY tblAlt.altText;
Or use MySqlism, might be faster:
SELECT
tblAlt.altText,
Count(tblAnswers.answerID), #total_count as total_count
FROM tblAlt
cross join (SELECT #total_count := COUNT(answerID) FROM tblAnswers) as x
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questionID = " & CInt(questionID) & "
GROUP BY tblAlt.altText;
Or you can use multi-statements. Note, SET statements doesn't appear on ADO.NET's DataReader or DataTable. ADO.NET can still get the results from your actual query. This has a certainty to be faster among all approaches:
SET #total_count := (SELECT COUNT(answerID) FROM tblAnswers);
SELECT
tblAlt.altText,
Count(tblAnswers.answerID), #total_count as total_count
FROM tblAlt
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questionID = " & CInt(questionID) & "
GROUP BY tblAlt.altText;

Answer 2

you can use an subquery to do this, something like:
SELECT
tblAlt.altText,
Count(tblAnswers.answerID),
(SELECT COUNT(answerID) FROM tblAnswers) as total_count
FROM tblAlt
LEFT JOIN tblAnswers ON (tblAlt.altId = tblAnswers.altID)
WHERE tblAlt.questionID = " & CInt(questionID) & "
GROUP BY tblAlt.altText;
Some Resources:
http://beginner-sql-tutorial.com/sql-subquery.htm
http://www.1keydata.com/sql/sql-subquery.html