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 uses the following precedence order for data types:

1. user-defined data types (highest)
   
2. sql_varian t
   
3. xml
   
4. datetimeoffset
   
5. datetime2
   
6. datetime
   
7. smalldatetime
   
8. date
   
9. time
   
10. float
    
11. real
    
12. decimal
    
13. money
    
14. smallmoney
    
15. bigint
    
16. int
    
17. smallint
    
18. tinyint
    
19. bit
    
20. ntext
    
21. text
    
22. image
    
23. timestamp
    
24. uniqueidentifier
    
25. nvarchar (including nvarchar(max) )
    
26. nchar
    
27. varchar (including varchar(max) )
    
28. char
    
29. varbinary (including varbinary(max) )
    
30. binary (lowest)