To answer this question, you need to understand the `SUBSTRING`

function in SQL.

The `SUBSTRING`

function is used to extract a substring from a given string. It takes three arguments: the input string, the starting position, and the length of the substring to be extracted.

In this case, the input string is '123456'. The starting position is 0, and the length is 3.

Using these arguments, the `SUBSTRING`

function will extract a substring starting from the 0th position (which is the first character) with a length of 3 characters.

So, the output of the `SUBSTRING('123456', 0, 3)`

statement will be '12'.

Therefore, the correct answer is B) 12.