Final answer:
The query SELECT 123+'123' AS Result performs arithmetic addition in a system like MySQL, resulting in 246. Option A is correct since the string '123' is implicitly converted to a numeric 123 before addition.
Step-by-step explanation:
When executing the SQL query SELECT 123+'123' AS Result, the database management system will attempt to perform implicit type conversion, typically casting the string '123' to a numeric value if possible, and then adding the two numbers together. The expected behavior, in a system like MySQL, is an arithmetic addition. Thus, the answer would be 246, as the database converts the string '123' into a numeric 123 and then adds it to the other numeric 123.
Option A is correct here, whereas option B would be correct if it were a string concatenation operation instead. An error message (option C) is unlikely unless the system has strict casting rules that prevent automatic conversion, and option D (None of the above) would not be applicable since option A is indeed the right answer.