Replace `0` with `N/A` or `-1` in pivot query result - sql

Question

I have Attendance table in which date and attendance is stored and I am passing date range in this query to display attendance report.
Now my question is how can I replace 0 (which I am getting as a output if the date passsed doesn't match with the date inside the Attendance table) with N/A or -1 ?
SET #query = 'SELECT RollNo,FirstName,LastName, ' + #cols + ' from
(
select S.RollNo,U.FirstName,U.LastName,
D.startdate,
convert(CHAR(10), startdate, 120) PivotDate
from #tempDates D,Attendance A, Student S, UserDetails U
where D.startdate = A.Date and A.EnrollmentNo=S.EnrollmentNo and A.EnrollmentNo=U.userID
) x
pivot
(
count(startdate)
for PivotDate in (' + #cols + ')
) p '

Answer 1

You could use CASE as Brandon Miller suggested. Here's another option - you can use NULLIF to replace a zero with a null value, and then replace any null value with N/A. You'll need to create a 2nd variable to represent your columns in the select statement of your dynamic query. Here's a full example with test data:
-- test data
create table #tempDates (startdate date)
create table Attendance (date date, enrollmentno int)
create table Student (rollno int, enrollmentno int)
create table UserDetails (FirstName varchar(10), LastName varchar(10), userid int)
insert into #tempDates values ('1/1/2018')
insert into Attendance values ('1/1/2018', 1)
insert into Student values (1, 1)
insert into UserDetails values ('J', 'S', 1)
declare #cols varchar(100) = '[2018-01-01],[2018-01-02]'
declare #cols_select varchar(500) = 'ISNULL(NULLIF(CAST([2018-01-01] AS VARCHAR(10)), ''0''), ''N/A'') AS [2018-01-01],ISNULL(NULLIF(CAST([2018-01-02] AS VARCHAR(10)), ''0''), ''N/A'') AS [2018-01-02]'
DECLARE #query nvarchar(max)
SET #query = 'SELECT RollNo,FirstName,LastName, '
+ #cols_select
+ 'from
(
select S.RollNo,U.FirstName,U.LastName,
D.startdate,
convert(CHAR(10), startdate, 120) PivotDate
from #tempDates D,Attendance A, Student S, UserDetails U
where D.startdate = A.Date and A.EnrollmentNo=S.EnrollmentNo and A.EnrollmentNo=U.userID
) x
pivot
(
count(startdate)
for PivotDate in (' + #cols + ')
) p '
EXEC sp_executesql #query
Outputs:
RollNo FirstName LastName 2018-01-01 2018-01-02
1 J S 1 N/A
For fun, here's a function you can use to convert the #cols variable to the #cols_select variable:
create function dbo.fn_convert_cols(#cols varchar(max)) returns varchar(max)
as
begin
declare #col varchar(20)
declare #cols_select varchar(max) = ''
declare #idx int, #idx2 int
select #idx = CHARINDEX('[', #cols), #idx2 = CHARINDEX(']', #cols)
while #idx > 0 and #idx2 > 0
begin
select #col = SUBSTRING(#cols, #idx + 1, #idx2 - #idx - 1)
select #cols_select += ',ISNULL(NULLIF(CAST([' + #col + '] AS VARCHAR(10)), ''0''), ''N/A'') AS [' + #col + ']'
select #cols = SUBSTRING(#cols, #idx2 + 1, len(#cols) - #idx2)
select #idx = CHARINDEX('[', #cols), #idx2 = CHARINDEX(']', #cols)
end
select #cols_select = SUBSTRING(#cols_select, 2, len(#cols_select) - 1)
return #cols_select
end
go
So now you can just call the function when you're building the query, like this:
SET #query = 'SELECT RollNo,FirstName,LastName, ' + dbo.fn_convert_cols(#cols)+ ' from