MySQL IFNULL syntax on outer query to return a record when query does not return any records

Question

I'm looking for guidance on how to apply IFNULL to an outer query in my mySQL Query. The query checks for new timecards submitted the previous day and kicks off a procedure that writes the results to a file server. Frequently there are no records but we still need to send a file with a record showing "no data". I believe the best solution is IFNULL but my syntex results in an error. Below is my raw query without the IFNULL outer query. Any help with syntex would be greatly appreciated.

SELECT 
    CONCAT(r.first_name, ' ', r.last_name) 'Name',
    e.eng_no AS 'ENG_ID',
    eb.po_number AS 'PO_NUMBER',
    ne.org_name AS 'Supplier',
    uv.full_name AS 'Timecard_Approver',
    eb.po_line_number AS 'PO_Line_No',
    rt.ext_project_code AS 'Ext_Project_Code',
    rt.day_date AS 'Timecard_Date',
    rt.job_work_site AS 'Job_Work_Site',
    rt.worked_hours AS 'Total_Hours'
FROM
    raw_tcd_agg rt
        JOIN
    eng e ON rt.eng_id = e.id
        JOIN
    res r ON r.id = e.res_id
        JOIN
    eng_brt eb ON eb.id = e.cur_eng_brt_id
        AND eb.eng_id = e.id
        JOIN
    cli_ctr cc ON cc.net_id = e.net_id
        AND cc.id = eb.cli_ctr_id
        JOIN
    usr_viw uv ON e.cli_usr_id_tcd_approver = uv.id
        LEFT JOIN
    net_ent ne ON e.ven_net_ent_id = ne.id
WHERE
    e.net_id = 100
        AND e.cli_net_ent_id = 1234
        AND rt.day_date IN (SELECT 
            rtm.day_date
        FROM
            raw_tcd_agg rtm
                JOIN
            eng e2 ON e2.id = rtm.eng_id
        WHERE
            e2.net_id = 100
                AND e2.cli_net_ent_id = 1234
                AND rt.day_date = DATE_SUB(CURRENT_DATE(), INTERVAL 1 DAY))

Answer 1

use CONCAT_WS to concatenate the first and last name with a space in the middle - result will be NULL if both first and last name are NULL. Then use COALESCE to substitute NULL with N/A. HTH!

COALESCE(CONCAT_WS(' ', r.first_name, r.last_name), 'N/A') as Name