Collation issue while join query in MVC5 and SQL Server 2012 - sql-server

Question

When I join two tables I got a collation issue that is
System.Data.SqlClient.SqlException: Cannot resolve the collation conflict between "SQL_Latin1_General_CP1_CI_AS" and "Latin1_General_CI_AI" in the equal to operation.
Then I set the collation in my db using the following code
ALTER DATABASE [CAM] COLLATE SQL_Latin1_General_CP1_CI_AS;
ALTER TABLE CAM_Users
ALTER COLUMN [EmployeeCode] VARCHAR(50)
COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL;
But I still get the same error.
My join query is this:
List<DTOUserManagement> users = (from CAMuser in _unitOfWorkAsync.RepositoryAsync<CAM_Users>().Queryable()
join QRuser in _unitOfWorkAsync.RepositoryAsync<CAM_V_EmployeeMaster>().Queryable() on CAMuser.EmployeeCode equals QRuser.EmployeeCode into t
from t1 in t.DefaultIfEmpty()
join CAMDomain in _unitOfWorkAsync.RepositoryAsync<CAM_Domain>().Queryable() on CAMuser.DomainID equals CAMDomain.DomainID into t2
from t3 in t2.DefaultIfEmpty()
where CAMuser.IsActive
select new DTOUserManagement
{
TransactUserCode = CAMuser.TransactUserCode,
EmployeeCode = CAMuser.EmployeeCode,
EmployeeName = t1.EmployeeName,
Email = t1.EMail,
DomainID = CAMuser.DomainID,
DomainName = t3.DomainName,
IsActive = CAMuser.IsActive,
AssignedRole = CAMuser.AssignedRoles
}).ToList();
How can I solve this?
Please reply anybody

Answer 1

The problem here is that the COLLATION must match on joining columns.
There are two ways to fix this. First you could change the collation on each column. Or second, you can change the collation at execution time. Here's an example of the second approach:
Sample Data
/* T1 and T2 are identical tables in structre and content, except
* for the collation.
*/
DECLARE #T1 TABLE
(
ID VARCHAR(3) COLLATE SQL_Latin1_General_CP1_CI_AS
)
;
DECLARE #T2 TABLE
(
ID VARCHAR(3) COLLATE Latin1_General_CI_AI
)
;
INSERT INTO #T1
(
ID
)
VALUES
('x'),
('y'),
('z')
;
INSERT INTO #T2
(
ID
)
VALUES
('x'),
('y'),
('z')
;
Anti Pattern - Will not Work
/* This query will failed with the error:
* Cannot resolve the collation conflict between "Latin1_General_CI_AI" and "SQL_Latin1_General_CP1_CI_AS" in the equal to operation.
*/
SELECT
*
FROM
#T1 AS t1
INNER JOIN #T2 AS t2 ON t1.ID = t2.ID
;
Corrected - No Error
/* Success.
*/
SELECT
*
FROM
#T1 AS t1
INNER JOIN #T2 AS t2 ON t1.ID = t2.ID COLLATE Latin1_General_CI_AI
;

Answer 2

You need to check your tables that are involved in these JOINs here to verify that all columns involved have the same collation.
You can do this with this SQL query:
SELECT
TableName = t.Name,
ColumnName = c.name,
Collation = c.collation_name
FROM
sys.columns c
INNER JOIN
sys.tables t ON t.object_id = c.object_id
INNER JOIN
sys.types ty ON c.system_type_id = ty.system_type_id
WHERE
t.name IN ('CAM_Users', 'CAM_Domain') -- add any further tables to check
AND ty.name IN ('char', 'nchar', 'nvarchar', 'varchar')
ORDER BY
t.name, c.name
If there are columns that do not match the database default collation, you need to change those to be the same as all other columns. Once all the string columns in those tables are the same collation, then your joins should work.
Update: use this query to find those tables & columns that do not have the current default database collation:
SELECT
TableName = t.Name,
ColumnName = c.name,
Collation = c.collation_name
FROM
sys.columns c
INNER JOIN
sys.tables t ON t.object_id = c.object_id
INNER JOIN
sys.types ty ON c.system_type_id = ty.system_type_id
WHERE
ty.name IN ('char', 'nchar', 'nvarchar', 'varchar')
AND c.collation_name <> 'SQL_Latin1_General_CP1_CI_AS'
ORDER BY
t.name, c.name