Question

Table structure:

Table Structure http://imagebin.org/index.php?mode=image&id=238883

I want to fetch data from both the tables which satisfy some of the conditions like

    WHERE batch='2009', sex='male',course='B.Tech', branch='cs', xth_percent>60, 
     x2percent>60, gradpercent>60 and (if ranktype='other' ) then 
     no._of_not_null_semester>number elseifranktype='Leet') then 
     no._of_not_null_semester>number-2

sem 1-8 contains percentage for 8 semesters, and I want to filter results for each student if they have cleared 3 semesters or 4 semester i.e. not null values out of 8 values

 no._of_not_null_semester 

needs to be calculated, it is not a part of database, need help with that as well.

Required Query

             SELECT * FROM student_test 
                      INNER JOIN master_test ON student_test.id=master_test.id 
                      WHERE sex='male' and batch='2009' and course='B.Tech' 
                      and xthpercent>60 and x2percent>60 and 
                      WHEN ranktype='Leet' THEN 
                              SUM(CASE WHEN sem1 IS NOT NULL THEN 1 ELSE 0
                                  WHEN sem2 IS NOT NULL THEN 1  ELSE 0
                                  WHEN sem3 IS NOT NULL THEN 1 ELSE 0
                                  WHEN sem4 IS NOT NULL THEN 1  ELSE 0
                                  WHEN sem5 IS NOT NULL THEN 1  ELSE 0) >2
                      ELSE 
                             SUM(CASE WHEN sem1 IS NOT NULL THEN 1 ELSE 0
                                 WHEN sem2 S NOT NULL THEN 1  ELSE 0
                                  WHEN sem3 IS NOT NULL THEN 1 ELSE 0
                                  WHEN sem4 IS NOT NULL THEN 1  ELSE 0
                                  WHEN sem5 IS NOT NULL THEN 1  ELSE 0) >4

Answer 1

Without changing the structure you can’t use COUNT to achieve this.

One way to solve the problem would be to create a semester table which would contain a row for each finished semester for each student. This would have a foreign key pointing to test_student.id and you could use COUNT(semester.id)

If that is an option for you, it would be the best solution.

EDIT:

Check this out, didn’t test the query but should work generally
I decided to do the math in the select itself to prevent calculating the same thing twice.
The HAVING conditions are applied after your result is ready to deliver, just before a LIMIT.
In terms of speed optimization you could try and move the sSum block into the WHERE condition just like you had it before. Probably it doesn’t make much of a difference

SUM() does not work because it is an aggregate function which summarizes values in a column

I did some changes to your query in addition:

• don’t SELECT *, select specific fields and add a table identifier. ( in this case I used the aliases s for student_test AND m for master_test )
• you put s.batch = '2009' into single quotes – if the field batch is an integer field, you should use s.batch = 2009, which would prevent MySQL from casting every single row to string to be able to compare it (int = int much faster than cast(int as varchar) = varchar) same about the other numeric values in your table

The Query:

SELECT
    s.id,
    s.sex,
    s.course,
    s.branch,
    ( 
        IF ( m.sem1 IS NOT NULL, 1, 0 ) +
        IF ( m.sem2 IS NOT NULL, 1, 0 ) +
        IF ( m.sem3 IS NOT NULL, 1, 0 ) +
        IF ( m.sem4 IS NOT NULL, 1, 0 ) +
        IF ( m.sem5 IS NOT NULL, 1, 0 ) +
        IF ( m.sem6 IS NOT NULL, 1, 0 ) +
        IF ( m.sem7 IS NOT NULL, 1, 0 ) +
        IF ( m.sem8 IS NOT NULL, 1, 0 )
    ) AS sSum
FROM
    student_test s
        INNER JOIN master_test m ON m.id = s.id
WHERE
    s.sex = 'male'
    AND
    s.batch = '2009' # I dont see this field in your database diagram!?
    AND
    s.course = 'B.Tech'
    AND
    m.xthpercent > 60
    AND
    m.x2percent > 60
HAVING
    (
        m.ranktype = 'OTHER'
        AND
        sSum > 4
    )
    OR
    (
        m.ranktype = 'LEET'
        AND
        sSum > 2
    )

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