Why cast/convert from int returns an asterisk

Question

Someone recently asked me this question and I thought I\'d post it on Stack Overflow to get some input.

Now obviously both of the following scenarios are supposed to

Answer 1

For even more fun, try this one:

DECLARE @i INT
SET @i = 100
SELECT CAST(@i AS VARCHAR(2)) -- result: '*'
go

DECLARE @i INT
SET @i = 100
SELECT CAST(@i AS NVARCHAR(2)) -- result: Arithmetic overflow error

:)

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The answer to your query is: "Historical reasons"

The datatypes INT and VARCHAR are older than BIGINT and NVARCHAR. Much older. In fact they're in the original SQL specs. Also older is the exception-suppressing approach of replacing the output with asterisks.

Later on, the SQL folks decided that throwing an error was better/more consistent, etc. than substituting bogus (and usually confusing) output strings. However for consistencies sake they retained the prior behavior for the pre-existing combinations of data-types (so as not to break existing code).

So (much) later when BIGINT and NVARCHAR datatypes were added, they got the new(er) behavior because they were not covered by the grandfathering mentioned above.

Answer 2

You can read on the CAST and CONVERT page on the "Truncating and Rounding Results" section. Int, smallint and tinyint will return * when the result length is too short to display when converted to char or varchar. Other numeric to string conversions will return an error.