Implicit conversion of varchar value to varchar - collation conflict - sql-server

Question

I'm getting the following error whilst running this script. I've tried using the following:
COLLATE Latin1_General_CI_AS. Please can it be sorted? Thanks
Msg 457, Level 16, State 1, Line 8
Implicit conversion of varchar value to varchar cannot be performed because the collation of the value is unresolved due to a collation conflict
DECLARE #AccountID INT
SET #AccountID = 12
SELECT TOP 1 ac.AccountID,
co.Email,
ao.AccountOptionID
FROM CRM.acc.Account ac
INNER JOIN CRM.[profile].[Profile] pr
ON pr.ProfileID = ac.ProfileFK
INNER JOIN CRM.[profile].Contact co
ON pr.ProfileID = co.ProfileFK
LEFT JOIN CRM.acc.[AccountOption] ao
ON ao.AccountFK = ac.AccountID
LEFT JOIN (
SELECT OptionID
FROM CRM.acc.[Option]
WHERE [Name] = 'SMS messages') op
ON op.OptionID = ao.OptionFK
WHERE ac.AccountID = #AccountID
UNION ALL
SELECT u.UnsubscribeID,
u.EmailAddress,
u.SentEmailFK
FROM Email.dbo.Unsubscribe u
INNER JOIN (
SELECT CASE
WHEN AccountTypeFK = 2 THEN OnlineBillingEmail
ELSE EmailBillingEmail
END [EmailAddress]
FROM CRM.acc.Account
WHERE AccountID = #AccountID
) ace
ON ace.EmailAddress COLLATE DATABASE_DEFAULT = u.EmailAddress COLLATE DATABASE_DEFAULT
WHERE ISNULL(ace.EmailAddress, '') != ''

Answer 1

Seems that you have different collation types on your database. Then you can have issues when joining tables or to tables in other databases, as in this case. To get around this you can specify the collation of columns or force a collation using the COLLATE clause when joining two columns. Check more info about collation in MSDN
Also you need to specify the COLLATE clause where you are using the problematic column(s). Check this answer, it answer a very similar question
It is better to stick to a single collation globally. Otherwise you will have problems.
See a detailed explanation of the different collation styles
Edited: to check column collation use this snippet
SELECT name, collation_name
FROM sys.columns
WHERE OBJECT_ID IN (SELECT OBJECT_ID
FROM sys.objects
WHERE type = 'U'
AND name = 'your_table_name'
)
AND name = 'your_column_name'
Edited: added snippet to get all columns with different collation on a database
SELECT [TABLE_NAME] = OBJECT_NAME([id]),
[COLUMN_NAME] = [name],
[COLLATION_NAME] = collation
FROM syscolumns
WHERE collation <> 'your_database_collation_type'
AND collation IS NOT NULL
AND OBJECTPROPERTY([id], N'IsUserTable')=1

Answer 2

try this
ace.EmailAddress COLLATE Latin1_General_CI_AS = u.EmailAddress COLLATE Latin1_General_CI_AS

Answer 3

Because you are doing a union all to the CRM table which has a different collation. You need to explicitly define the collation of your columns going into your union. In your case that will be UnsubscribeID,EmailAddress and SentEmailFK all should be defined with collate database_default
Running the below should work. Let me know in the comments if this works
SELECT TOP 1 ac.AccountID,
co.Email,
ao.AccountOptionID
FROM CRM.acc.Account ac
INNER JOIN CRM.[profile].[Profile] pr
ON pr.ProfileID = ac.ProfileFK
INNER JOIN CRM.[profile].Contact co
ON pr.ProfileID = co.ProfileFK
LEFT JOIN CRM.acc.[AccountOption] ao
ON ao.AccountFK = ac.AccountID
LEFT JOIN (
SELECT OptionID
FROM CRM.acc.[Option]
WHERE [Name] = 'SMS messages') op
ON op.OptionID = ao.OptionFK
WHERE ac.AccountID = #AccountID
UNION ALL
SELECT u.UnsubscribeID COLLATE DATABASE_DEFAULT AS UnsubscribeID,
u.EmailAddress COLLATE DATABASE_DEFAULT AS EmailAddress ,
u.SentEmailFK COLLATE DATABASE_DEFAULT AS SentEmailFK
FROM Email.dbo.Unsubscribe u
INNER JOIN (
SELECT CASE
WHEN AccountTypeFK = 2 THEN OnlineBillingEmail
ELSE EmailBillingEmail
END [EmailAddress]
FROM CRM.acc.Account
WHERE AccountID = #AccountID
) ace
ON ace.EmailAddress COLLATE DATABASE_DEFAULT = u.EmailAddress COLLATE
DATABASE_DEFAULT
WHERE ISNULL(ace.EmailAddress, '') != ''