multiple count from multiple tables and also group by grade - mysql

Question

i have table with student_uid,grade,test_name as columns i want to count how many got each grade..for this
SELECT a.grade,COUNT(a.grade) AS count1
FROM 2015_2016_x_english_grades AS a
where test_name='ut1_marks'
GROUP BY grade
for single table worked how to do it for more than one table
my query:
SELECT a.grade, COUNT(a.grade),b.grade,COUNT(b.grade)
FROM 2015_2016_x_english_grades a
INNER JOIN 2015_2016_x_hindi_grades b ON a.grade=b.grade
WHERE a.test_name = b.ut1_marks='ut1_marks'
GROUP BY a.grade,b.grade
what is wrong in this?
i also tried this
SELECT a.grade,COUNT(a.grade),(SELECT COUNT(b.grade)FROM 2015_2016_x_biology_grades b where b.test_name='ut1_marks' GROUP BY b.grade)as count1 FROM 2015_2016_x_biology_grades a where test_name='ut1_marks' GROUP BY a.grade
it says [Err] 1242 - Subquery returns more than 1 row

Answer 1

Do the counting in subqueries, and join the subqueries.
SELECT e.grade, english_count, hindi_count
FROM (SELECT grade, COUNT(*) AS english_count
FROM 2015_2016_x_english_grades
WHERE test_name = 'ut1_marks'
GROUP BY grade) AS e
JOIN (SELECT grade, COUNT(*) as hindi_count
FROM 2015_2016_x_hindi_grades
WHERE test_name = 'ut1_marks'
GROUP BY grade) AS h
ON e.grade = h.grade
Or if there's a unique key in each table, you can do:
SELECT e.grade, COUNT(DISTINCT e.id) AS english_count, COUNT(DISTINCT h.id) AS hindi_count
FROM 2015_2016_x_english_grades AS e
JOIN 2015_2016_x_hindi_grades AS h ON e.grade = h.grade AND e.test_name = h.test_name
WHERE e.test_name = 'ut1_marks'
GROUP BY e.grade
Note that both of these queries will only show a grade if it exists in both tables. To get grades that only exist in one table, you need a FULL OUTER JOIN, but MySQL doesn't have this operation. See
Full Outer Join in MySQL
for how to emulate them.