Concatenate SQL Case Expression

Question

So I'm trying to combine values in each new column that I created in view with a case statement. How would I go about doing this?

SELECT
    PI.Patient_UID, PI.FirstName, PI.LastName, 
    AP.ApptStatus, AP.VisitPosted, CD.TotalDue,
    AP.Appointment_UID,
    CASE 
        WHEN AP.VisitPosted = 0 
            THEN 'Visit Posted Error' 
    END Error1,
    CASE 
        WHEN (CD.TotalDue IS NULL OR CD.TotalDue = '')  
            THEN 'Gross Charge Error' 
    END Error2
FROM
    vw_ODBC_pt_PatientInfo AS PI
INNER JOIN
    vw_ODBC_appts_Appointments AS AP ON AP.PatientFID = PI.Patient_UID
INNER JOIN
    vw_ODBC_actv_ChargeDetail AS CD ON CD.PatientFID = PI.Patient_UID 
WHERE
    AP.ApptStatus NOT IN ('10', '11', '12');

I need the new columns Error1 and Error2 to be concatenated as such:

Error1                Error2               ErrorsCombined
Visit Posted Error    Gross Charge Error    Visit Posted Error;Gross Charge Error
Visit Posted Error    NULL                  Visit Posted Error;
Visit Posted Error    NULL                  Visit Posted Error;
Visit Posted Error    NULL                  Visit Posted Error;

Any help would be greatly appreciated! Thanks in advance.

Answer 1

use APPLY operator for the Error1 and Error2 expression. Make use of concat_ws() which perform string concatenation with separator and it handle NULL value.

select PI.Patient_UID, 
       PI.FirstName, 
       PI.LastName, 
       AP.ApptStatus, 
       AP.VisitPosted, 
       CD.TotalDue,
       AP.Appointment_UID,
       e.Error1,
       e.Error2,
       concat_ws(';', e.Error1, e.Error2) as ErrorsCombined
from  vw_ODBC_pt_PatientInfo as PI
inner join vw_ODBC_appts_Appointments as AP on AP.PatientFID = PI.Patient_UID
inner join vw_ODBC_actv_ChargeDetail  as CD on CD.PatientFID = PI.Patient_UID 
cross apply
(
    select case when AP.VisitPosted = 0 
                then 'Visit Posted Error' 
                end as Error1,
           case when (CD.TotalDue is null or CD.TotalDue = '') 
                then 'Gross Charge Error' 
                end as Error2
) e
where AP.ApptStatus not in ('10','11','12');