When an operator combines two expressions of different data types, the rules for data type precedence specify that the data type with the lower precedence is converted to the data type with the higher precedence. If the conversion is not a supported implicit conversion, an error is returned. When both operand expressions have the same data type, the result of the operation has that data type.

SQL Server 2005 uses the following precedence order for data types:

1. user-defined data types (highest)
   
2. sql_variant
   
3. xml
   
4. datetime
   
5. smalldatetime
   
6. float
   
7. real
   
8. decimal
   
9. money
   
10. smallmoney
    
11. bigint
    
12. int
    
13. smallint
    
14. tinyint
    
15. bit
    
16. ntext
    
17. text
    
18. image
    
19. timestamp
    
20. uniqueidentifier
    
21. nvarchar (including nvarchar(max) )
    
22. nchar
    
23. varchar (including varchar(max) )
    
24. char
    
25. varbinary (including varbinary(max) )
    
26. binary (lowest)
    

 See Also

Reference

Data Types (Transact-SQL)
Expressions (Transact-SQL)
CAST and CONVERT (Transact-SQL)

Help and Information

Getting SQL Server 2005 Assistance