Finding row causing error in type conversion in SQL Server - sql

Question

I am trying to cast a column as smalldatetime from varchar. There are some rows containing errors, how can I find them?
SELECT
PA.EAR_TAG
,ISNULL(B.DISPOSAL_DATE, H.DISPOSAL_DATE) as HB_Date
,Y.[DATE OF MOVEMENT] as Y_Date
,DATEDIFF(DAY, ISNULL(B.DISPOSAL_DATE, H.DISPOSAL_DATE), cast(Y.[DATE OF MOVEMENT] as smalldatetime))
FROM
DairyTelomere.dbo.PROJECT_ANIMALS AS PA
LEFT JOIN
Langhill.dbo.YOUNG_STOCK_BULL AS B ON Pa.EAR_TAG = B.EAR_TAG
LEFT JOIN
Langhill.dbo.YOUNG_STOCK_HEIFER AS H ON PA.EAR_TAG = H.EAR_TAG
LEFT JOIN
DairyTelomere.dbo.Young_Stock_culls AS Y ON PA.EAR_TAG = Y.Ear_Tag
The error I get is:
Msg 242, Level 16, State 3, Line 1
The conversion of a varchar data type to a smalldatetime data type resulted in an out-of-range value.
I know that if the column was in a date format I could check it by using ISDATE() but unfortunately I can't change the column type (don't have permissions).
Any ideas will be greatly appreciated.

Answer 1

you can use the isdate to get a list of all the ones that are not converting for you. You dont need to change the column type to use this so i am confused by your statement
if the column was in a date format I could check it by using ISDATE() but unfortunately I can't change the column type (don't have permissions)
Will help more if you can clarify but this query should get you a list of rows that have bad date values.
select table.date_as_varchar
from table
where isdate(table.date_as_varchar) = 0

Answer 2

adding to #workabyte answer you can also try using TRY_PARSE, TRY_CAST OR TRY_CONVERT, all of them return NULL if the conversion failed, that way you can know wich rows caused the error.
TRY_PARSE
as the documentation says:
Use TRY_PARSE only for converting from string to date/time and number
types. For general type conversions, continue to use CAST or CONVERT.
Keep in mind that there is a certain performance overhead in parsing
the string value.
Usage example:
SELECT TRY_PARSE(your_date AS DATETIME USING 'es-ES') as date
FROM your_table
es-ES is a culture parameter,different culture paramaters yield different results in your conversions, you can find the full list of parameters in the documentation
TRY_CONVERT
as the documentation says:
TRY_CONVERT takes the value passed to it and tries to convert it to
the specified data_type. If the cast succeeds, TRY_CONVERT returns the
value as the specified data_type; if an error occurs, null is
returned. However if you request a conversion that is explicitly not
permitted, then TRY_CONVERT fails with an error.
Usage example:
SELECT TRY_CONVERT(DATETIME,your_date,103) as date
FROM your_table
The 103 being the style/format of the date you are converting, here you can find a list of the formats avaliable
TRY_CAST
as the documentation says:
TRY_CAST takes the value passed to it and tries to convert it to the
specified data_type. If the cast succeeds, TRY_CAST returns the value
as the specified data_type; if an error occurs, null is returned.
However if you request a conversion that is explicitly not permitted,
then TRY_CAST fails with an error.
Usage example:
SELECT TRY_CAST(your_date AS DATETIME) as date
FROM your_table