CODEWITHSUNDEEP
sqlsql-serverleft-join
Adam Levitt
Adam Levitt

Reputation: 10476

SQL LEFT JOIN finding non-zero value as zero

I have the following query with many LEFT JOIN clauses that has 7 result columns, the last two of which are numbers. I'm expecting the count_non_zero column to always be equal to the count_total column (given the data I current have)

WITH temp_table AS ( 
SELECT 
    attr.company_name_id AS option_id, 
    attr.company_name AS option_name, 
    uj.internship_company_name_id, 
    AVG(CASE WHEN s.salary > 0 THEN s.salary END) AS average, 
    COUNT(CASE WHEN s.salary > 0 THEN attr.company_name END) as count_non_zero, 
    COUNT(attr.company_name_id) as count_total 
FROM company_name attr 
    LEFT JOIN user_job_internship uj ON uj.internship_company_name_id = attr.company_name_id 
        AND attr.approved_by_administrator = 1 
    LEFT JOIN salary_internship s ON uj.user_job_internship_id = s.user_job_id 
        AND uj.job_type_id = 4 
    LEFT JOIN [user] u ON u.user_id = uj.user_id AND u.include_in_student_site_results = 1  
        AND u.site_instance_id IN (1) 
    LEFT JOIN user_education_mba_school mba ON u.user_id = mba.user_id  
        AND mba.mba_graduation_year_id NOT IN (8)  
GROUP BY attr.company_name_id, attr.company_name, uj.internship_company_name_id)
SELECT * FROM (SELECT ROW_NUMBER() OVER (ORDER BY average DESC) AS row, * 
FROM temp_table WHERE count_total >= 3) sub 
WHERE row >= 1 AND row <= 25 ORDER BY average DESC;

I run this query to prove that no values in the 'salary' column are returning a value of 0.

SELECT s.* FROM user_job_internship uj, salary_internship s 
where internship_company_name_id = 440
AND uj.user_job_internship_id = s.user_job_id

I'm thinking there is something that messes up the results that is causing the count_non_zero to get counts that do not exist. Anyone have anythoughts?

Upvotes: 1

Views: 444

Answers (1)

dbenham
dbenham

Reputation: 130819

I am assuming your count_total is greater than your count_non_zero. That is to be expected because you are using outer join to join user_job_internship and salary_internship.

Your query is including companies that do not have any internships. A company will not be included in the count_non_zero if either the salary is 0 or if there is no internship at all.

Change those two joins to inner joins and you should get your expected result.

The other option is to change your count_total to ignore companies that haven't any internship

count(case when s.user_job_id is not null then attr.company_name_id end) as count_total

You have one other slight risk. Your count_non_zero is counting company_name whereas your count_total is counting company_name_id. You could have problems if the company_name column allows NULL values.

Upvotes: 2

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