Why does this query return a money value?

Question

Today I wrote a query that should return an error. Instead, it returns the value 15 with column name why and data type money. Do you have an idea why?

select \15why

Result:

why
15.00

Answer 1

You're specifying a constant:

money constants are represented as string of numbers with an optional decimal point and an optional currency symbol as a prefix

So select €15 results in a money constant, and so does select $15, as well as select ¥15.

There's a peculiarity as pointed out by Jeroen in the comments:

Because the yen sign (¥) is a currency indicator, and in some native Japanese character sets, its code point is the same as the one for backslash in ASCII.

See also MSDN: money and smallmoney (Transact-SQL).

So select \15 appears to be equal to select ¥15.

As for the column name: select 5a results in a column with the alias a and a value of 5. Because "a" is not a numeric suffix, it is treated as select 5 as a, where "as" is optional. Instead select 5e would return 5 in an unnamed column, because "e" is a numeric suffix.

So you've discovered a different way to write select ¥15 as why.