mysqlsqlqsqlquery

How can I do SQL query based on two conditions on two columns?


see the EARD scenario

Major_applied_for table

id preference application_number (fk) major_code (fk)
1 1 2 1
2 1 1 1
3 3 3 1
4 2 1 2
5 2 2 2

Some Clarifications:

• The code attribute of Major table holds (1)CS for computer science, (2)BMS for business management and so on.

• preference attribute of Major_Applied_For is 1, 2 or 3 (1 for being the first choice, 2 being the second choice and 3 being the third choice) . . .

This is a table that many to many relationship resolved in, I wanna get all the application numbers that have CS as the first choice and BMS as the second choice.

I tried this sql statement but it's logically incorrect.

SELECT m.id, CONCAT(m.fname, " ", m.lname) AS Fullname, app.number AS application_no FROM applicant m, application app, major_applied_for mjaf WHERE ((mjaf.major_code = 1 AND mjaf.preference = 1) AND (mjaf.major_code = 2 AND mjaf.preference = 2) AND (mjaf.application_number = app.number AND app.applicant_id = m.id));

How can I resolve this issue?


Solution

  • Find the applicants with CS as their first pref, find the applicants with BMS their second pref. Inner join these two sets and check their names.

    with first_cs as (
        select c.applicant_id
        from major_applied_for a inner join major b on a.major_code = b.code and a.preference = 1 and b.name = 'CS'
                                 inner join application c on a.application_number = c.number ), second_bms as(
        select c.applicant_id
        from major_applied_for a inner join major b on a.major_code = b.code and a.preference = 2 and b.name = 'BMS'
                                 inner join application c on a.application_number = c.number ) select fname,
           lname from first_cs a inner join second_bms b on a.applicant_id = b.applicant_id
                    inner join applicant c on a.applicant_id = c.id