Invalid operator for data type.The operator is add and the type is text.

Recently, when developing a file management system, I encountered another problem: the original local database was SQL2008, and there was a field SharedUserId of nvarchar(max) type.The query SQL statement uses...WHERE SharedUserId + ',' LIKE '%2,%', which can be executed normally.Later, I released the program to the space server I bought. The server is the database of SQL2000. Because SQL2000 does not have the nvarchar(max) type, I even changed it to the text type. As a result, the program reported an error when executing the same SQL statement:

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Microsoft Internet Explorer
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The operator is invalid for the data type.The operator is add and the type is text.(System.Exception)
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OK
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So, I even changed the local database field type to text, and then tested it, and a similar error was reported (even the SQL2008 is in English):

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Microsoft Internet Explorer
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The data types text and varchar are incompatible in the add operator.(System.Exception)
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OK
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After searching on the Internet, the original query statement was slightly modified (convert text to nvarchar and then perform + operation), and it worked:...WHERE SharedUserId + ',' LIKE '%2,%' is replaced by...WHERE CAST(SharedUserId AS NVARCHAR) + ',' LIKE '%2,%' or WHERE CONVERT(NVARCHAR, SharedUserId) + ',' LIKE '%2,%'