T-SQL CTE char() function not the same type as cast( as char)

Question

I wanted to create a small cte for the chars [az]. However if I use the char()-function for the recursive part like this:

with cte(chars)
as (
    select cast('a' as char) as chars
    union all
    select char(ascii(chars) + 1 ) from cte
    where chars < 'z'
)
select *
from cte

the data-types don't match even tho char() returns a char(1). But if the char()-function is casted to char(1), it runs perfectly fine:

with cte(chars)
as (
    select cast('a' as char) as chars
    union all
    select cast(char(ascii(chars) + 1 ) as char) from cte
    where chars < 'z'
)
select *
from cte

Am I missing something?

Answer 1

In SQL Server, never use char() (and related types) without a length. The default length varies by context -- and who wants to keep track of such things?

The following works:

with cte(chars) as (
      select cast('a' as char(1)) as chars
      union all
      select char(ascii(chars) + 1 ) from cte
      where chars < 'z'
     )
select *
from cte;

In other words, the default length for a char() in a cast() is different from the default length in a declare .