>then why here is an error?
> 
>SELECT CAST('123456789.23' as numeric) FROM RDB$DATABASE

Logically speaking I don't understand why

SELECT CAST('123456789.23' as numeric(9,0)) FROM RDB$DATABASE

is failing when

SELECT CAST('1.23' as numeric(1,0)) FROM RDB$DATABASE

succeeds.

Practically, I guess it means that Firebird first converts from a (var)char to an intermediate integer field before trying to round to nearest whole number, but I don't know why.

Normally, I don't store numbers in strings, and

SELECT CAST(123456789.23 as integer) FROM RDB$DATABASE

succeeds.

Here, I find that

SELECT CAST(123456789.12345678 as decimal) FROM RDB$DATABASE

succeeds, whereas

SELECT CAST(123456789.123456789 as decimal) FROM RDB$DATABASE

fails. I don't know why.

Sorry for not being able to shed any more light,
Set