Concatenating row values sql server 2008 r2 - sql-server-2008

Question

I have two tables register and att_bottom and I want to display only the students at a certain building who have been tardy based on today's date with the periods separated by a comma.
This is the way the data is displayed when joining both tables:
Student ID | Building | Period | Grade
12345 2 1 11
12345 2 5 11
43210 2 1 12
I want this:
Student ID | <u>Building | Period | Grade
12345 2 1,5 11
43210 2 1 12
This is my query:
select r.STUDENT_ID,
r.BUILDING ,
(select ab.attendancePeriod + ','
from att_bottom ab
where ab.STUDENT_ID = r.student_id
and ab.building = '2'
and ab.attendance_c ='T'
and ab.SCHOOL_YEAR =2014
CONVERT(date,ab.attendance_date,102) = convert(date,getdate(),102)
FOR XML PATH ('') ) AS PERIODS,
r.GRADE
FROM register r
where r.CURRENT_STATUS = 'A'
and r.BUILDING ='2'
I'm getting all the students at building 2 and even if they don't have an attedance_c of T; a NULL value for Periods is being retrieved:
Student ID | Building | Period | Grade
12345 2 1 , 5 11
43210 2 1 , 12
95687 2 NULL 09
78417 2 NULL 10
20357 2 NULL 11
I have tried and ab.attendancePeriod is Not NULL and I still get the same results.
Any thoughts?

Answer 1

The outer query doesn't listen to any filters in the subquery; it will return NULL for any rows that aren't matched by the join conditions. You need to filter differently. Here is one way (this also eliminates the errant trailing comma, and avoids comparing dates by converting them expensively to strings):
;WITH x AS
(
SELECT DISTINCT s = r.Student_ID, r.building,
p = ab.attendancePeriod, r.grade
FROM dbo.Register AS r
INNER JOIN dbo.att_bottom AS ab
ON r.Student_ID = ab.Student_ID
AND r.building = ab.building
WHERE ab.building = '2'
AND ab.attendance_c = 'T'
AND ab.SCHOOL_YEAR = 2014
AND ab.attendance_date >= CONVERT(DATE, GETDATE())
AND ab.attendance_date < DATEADD(DAY, 1, CONVERT(DATE, GETDATE()))
AND r.building = '2'
AND r.CURRENT_STATUS = 'A'
)
SELECT DISTINCT
[Student ID] = x.s,
x.building,
Period = STUFF((SELECT ',' + x2.p FROM x AS x2 WHERE x2.s = x.s
FOR XML PATH(''),
TYPE).value(N'./text()[]',N'nvarchar(max)'),1,1,''),
x.grade
FROM x;
Another way:
SELECT DISTINCT
r.Student_ID,
r.building,
Period = STUFF(b.p.value(N'./text()[1]', N'nvarchar(max)'),1,1,''),
r.grade
FROM dbo.Register AS r
CROSS APPLY
(
SELECT p = ',' + ab.attendancePeriod
FROM dbo.att_bottom AS ab
WHERE ab.building = '2'
AND ab.attendance_c = 'T'
AND ab.SCHOOL_YEAR = 2014
AND ab.attendance_date >= CONVERT(DATE, GETDATE())
AND ab.attendance_date < DATEADD(DAY, 1, CONVERT(DATE, GETDATE()))
AND ab.student_id = r.student_id
AND ab.building = r.building
FOR XML PATH(''),TYPE
) AS b(p)
WHERE b.p IS NOT NULL
AND r.building = '2'
AND r.CURRENT_STATUS = 'A';

Answer 2

Move the AS PERIODS select to be an inner join to r.