Why is 30 the default length for VARCHAR when using CAST?

Question

In SQL server 2005 this query

select len(cast(\'the quick brown fox jumped over the lazy dog\' as varchar))

returns 30 as length while the

Answer 1

I don't know why they chose 30, but it was the same in Sybase SQL Server, which Microsoft's SQL Server was developed from. It seems to be a peculiarity of those RDBMSs as it's not in the SQL standards, and other servers differ in their behaviour.