Cross Join and Left Outer Join of Tables in Database

Question

I have three table in my database

Employee Table

• EmployeeId (PK)
• Last Name

Question Table

• Qid (PK)
• Question

Questionnaire

• QuestionnaireId (PK)
• QId (FK)
• EmployeeId (FK)
• Response
• Details

This is the SQL Query that I write on my own, but it is producing an output that I do not need

 Select q.qid,e.employeeId, q.Question, eq.response 
 from employee e 
 cross join Question q
 left outer join employeequestionnaire eq on q.Qid= eq.Qid
 where e.employeeId = 1

This is the output

             Qid   EmployeeId        Question       Response 
             "1"       "1"          "Question1"     "0"
             "1"       "1"          "Question1"     "1"
             "2"       "1"          "Question2"     "1"
             "2"       "1"          "Question2"     "0"
             "3"       "1"          "Question3"     "1"
             "4"       "1"          "Question4"     NULL

But I need this kind of Output

             Qid    EmployeeId       Question       Response  
             "1"       "1"          "Question1"     "0"
             "2"       "1"          "Question2"     "1"
             "3"       "1"          "Question3"     "1"
             "4"       "1"          "Question4"     NULL

I am a newbie in SQL, sorry for my sample query..

Answer 1

Assuming the employeequestionnaire has the employeeID field, you don't need the employee table. I think you can just do:

Select q.qid, eq.employeeId, q.Question, eq.response 
from Question q left outer join
     employeequestionnaire eq
     on q.Qid= eq.Qid and
        eq.employeeId = 1

Notice that I moved the where clause into an on clause. This is sometimes necessary when using a left outer join .

If you wanted to include information about employees from that table, you would use not use a cross join :

Select q.qid, eq.employeeId, q.Question, eq.response 
from Question q left outer join
     employeequestionnaire eq
     on q.Qid= eq.Qid and
        eq.employeeId = 1 left outer join
     employees e
     on e.EmployeeID = eq.EmployeeID