SQL SELECT DISTINCT子查询错误：1241

Question

I am working on a long query that includes a SELECT DISTINCT and subquery. It is partially working, but not when put together. I am getting a Error: 1241 - Operand should contain 1 column(s) and I cannot see why. Any help would be greatly appreciated.

Here is my code:

SELECT p.projId, pc.company, s.staffId, s.fName, s.lName
    FROM projects AS p
    INNER JOIN projCorp AS pc ON p.projId = pc.projId
    INNER JOIN projStaff AS ps ON p.projId = ps.projId
    INNER JOIN staff AS s ON ps.staffId = s.StaffId
    WHERE p.projId = '9' AND s.company = pc.company
UNION
    SELECT DISTINCT p.projId, pc.company, "NA", "NA", "NA"
    FROM projects AS p
    INNER JOIN projCorp AS pc ON p.projId = pc.projId
    INNER JOIN projStaff AS ps ON p.projId = ps.projId
    WHERE p.projId = '9' AND pc.company NOT IN (SELECT p.projId, pc.company, s.staffId, s.fName, s.lName
        FROM projects AS p
        INNER JOIN projCorp AS pc ON p.projId = pc.projId
        INNER JOIN projStaff AS ps ON p.projId = ps.projId
        INNER JOIN staff AS s ON ps.staffId = s.StaffId
        WHERE p.projId = '9' AND s.company = pc.company);

Without the NOT IN subquery, I am getting this result:

The reason for the NOT IN subquery is to get rid of the third duplicate entry that doesn't have a staff member associated. The result should just have the first two entries from the picture result field.

Answer 1

Snip:

... WHERE p.projId = '9' AND pc.company NOT IN (
        SELECT p.projId, pc.company, s.staffId, s.fName, s.lName
        FROM projects AS p ....
    )

You're trying to select when company not in but there are specifying more than one selected row from within your not in query. Just select company :

... WHERE p.projId = '9' AND pc.company NOT IN (
        SELECT pc.company
        FROM projects AS p ....
    )

Answer 2

If you want to keep all the rows for a given projects, use a left join :

SELECT p.projId, pc.company, s.staffId, s.fName, s.lName
FROM projects p LEFT JOIN
     projCorp pc
     ON p.projId = pc.projId LEFT JOIN
     projStaff ps
     ON p.projId = ps.projId LEFT JOIN
     staff s
     ON ps.staffId = s.StaffId AND s.company = pc.company
WHERE p.projId = '9'; 

This seems more sensible than a complicated union query. You can use coalesce() to convert the NULL values to 'NA' , if that really is desirable.

I am a little confused on which table should go first -- but I'm thinking it is all companies as opposed to all projects. If so, this is the FROM clause with no WHERE :

FROM projCorp pc LEFT JOIN
     projects p   
     ON p.projId = pc.projId AND p.projId = '9' LEFT JOIN
     projStaff ps
     ON p.projId = ps.projId LEFT JOIN
     staff s
     ON ps.staffId = s.StaffId AND s.company = pc.company;

Answer 3

Your IN list should contain values from one column, pc.company. But your IN list contains values from multiple columns.