Conversion failed when converting date and/or time from character string - sql

Question

I am struggling with this query which returns the error: Conversion failed when converting date and/or time from character string.
This is a common error judging from my google searches, but nothing I've tried so far works. I've tried casting #startdate as datetime and varchar and leaving it alone, as in the below example.
I've also tried using convert against the fieldname and the parameter name, although admittedly, I may just be getting the syntax wrong.
ALTER PROCEDURE [dbo].[customFormReport]
(
#formid int,
#startdate DATETIME
)
AS
BEGIN
SET NOCOUNT ON
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME(fieldname) from FormResponse WHERE FormID = #formid AND value IS NOT NULL FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT FormID, FormSubmissionID,' + #cols + ' from
(
SELECT FormID, FormSubmissionID, fieldname, value
FROM FormResponse WHERE FormID = ' + CAST(#formid AS VARCHAR(25)) + ' AND createDate > ' + #startdate + '
) x
pivot
(
max(value)
for fieldname in (' + #cols + ')
) p '
execute(#query)
edit: the query works except when I add the bit causing the error:
' AND createDate > ' + #startdate + '

Answer 1

The problem is you are attempting to concatenate a datetime to your varchar sql string. You need to convert it:
convert(varchar(10), #startdate, 120)
So the full code will be:
ALTER PROCEDURE [dbo].[customFormReport]
(
#formid int,
#startdate DATETIME
)
AS
BEGIN
SET NOCOUNT ON
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME(fieldname) from FormResponse WHERE FormID = #formid AND value IS NOT NULL FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT FormID, FormSubmissionID,' + #cols + ' from
(
SELECT FormID, FormSubmissionID, fieldname, value
FROM FormResponse
WHERE FormID = ' + CAST(#formid AS VARCHAR(25)) + '
AND createDate > ''' + convert(varchar(10), #startdate, 120) + '''
) x
pivot
(
max(value)
for fieldname in (' + #cols + ')
) p '
execute(#query)

Answer 2

When you dynamically build the SQL Statement, the date value needs to be wrapped in single quotes. Whenever building a dynamic statement, do a SELECT #query and make sure the results look correct.
For your example, you would need to have 'WHERE createdate > ''' + covert(varchar(10), #startdate, 111) + '''
That would output: WHERE createdate > '2013/05/29'
Without the single quotes you would have: WHERE createdate > 2013/05/29