mysql query showing 9 results

Question

i have a problem.

I'm running following query. I have only one record in my database but i'm getting 9 results.

SELECT c.id, c.rk 
FROM cv AS c, employee AS e , cvCat AS cv_cat 
WHERE c.status=1 
    AND c.empIDFK = e.id 
    AND cv_cat.categoryFK IN ( 17,18,19,38,39,40,41,44,45,46 ) 
    AND cv_cat.cvFK = c.id

Can someone please let me know if they is any problem with this query. Why i'm getting 9 results rather then just 1 result.

This query should only display one record but its showing 9 results.

Answer 1

When you do

FROM cv AS c, employee AS e , cvCat AS cv_cat

You are doing an implicit join of the three tables. If you want to get distinct records you can add DISTINCT after your select:

SELECT DISTINCT c.id, c.rk 
FROM cv AS c, employee AS e , cvCat AS cv_cat 
WHERE c.status=1 
    AND c.empIDFK = e.id 
    AND cv_cat.categoryFK IN ( 17,18,19,38,39,40,41,44,45,46 ) 
    AND cv_cat.cvFK = c.id

Answer 2

Use explicit joins:

SELECT c.id, c.rk
FROM cv c
INNER JOIN employee e ON e.id = c.empIDFK
INNER JOIN cvCat cv_cat ON cv_cat.cvFK = c.id
WHERE c.status = 1
AND cv_cat.categoryFK IN (17,18,19,38,39,40,41,44,45,46)

Answer 3

I think the 9 result row "issue" is based on your JOIN syntax, as that kind of implicit join will return all rows (of each table) as a joined result, since you are only pulling out c.id and c.rk it may look like MySQL sent the same result back 9 times.

Side Note: Implicit joins are being deprecated, using explicit joins, such as...

    SELECT c.id, c.rk
    FROM cv c
    LEFT JOIN employee e ON c.empIDFK = e.id
    LEFT JOIN cvCat cv_cat ON c.id = cv_cat.cvFK
    WHERE...

Will help "future-proof" your code a bit and add a little more self-describing syntax to the whole query.