Question

I’m building a report for a database where I need to determine the number of “first scans” grouping by company, job, and date.

The scan table can contain multiple scans for the same item, however I only want to include the original scan in my COUNT, which can only be identified as being the scan with the earliest date that matches a particular item.

My first attempt at this was:

SELECT 
     _item_detail.job_id, 
     _item_group.group_id, 
     _scan.company_id, 
     DATE(scan_date_time) as scan_date, 
     COUNT(1)
FROM _scan
    INNER JOIN _item_detail ON _item_detail.company_id = _scan.company_id 
    AND 
    _item_detail.serial_number = _scan.serial_number
    INNER JOIN _item_group ON _item_group.group_id = _item_detail.group_id
WHERE _item_detail.job_id = '0326FCM' AND _scan.company_id = '152345' AND _item_group.group_id = 13
GROUP BY 
_item_detail.job_id, 
_item_group.group_id, 
_scan.company_id, scan_date -- first_scan_count
HAVING min(scan_date_time);

This is giving me incorrect results, though (about 3x too many). I am assuming it’s because the MIN record is being recalculated for each date, so if the min was found on day 1, it may also be found on day 3 and counted again.

How can I modify my query to achieve the desired results?

Answer 1

Something similar to this should work… I’m not completely sure of how your tables are laid out or how the data relates them together, but this is the general idea:

SELECT 
    _item_detail.job_id, 
    _item_group.group_id, 
    _scan.company_id, 
    DATE(scan_date_time) as scan_date, 
    COUNT(1)
FROM
    _scan s1
    INNER JOIN _item_detail 
        ON _item_detail.company_id = s1.company_id 
        AND _item_detail.serial_number = s1.serial_number
        AND _item_detail.job_id = '0326FCM'
    INNER JOIN _item_group 
        ON _item_group.group_id = _item_detail.group_id
        AND _item_group.group_id = 13
WHERE 
    s1.company_id = '152345'
    AND s1.scan_date_time = (
        SELECT MIN(s2.scan_date_time)
        FROM _scan s2
        WHERE 
            s2.company_id = s1.company_id
            AND s2.serial_number = s1.serial_number
    )
GROUP BY 
    _item_detail.job_id, 
    _item_group.group_id, 
    s1.company_id