您的第一个查询需要 SELECT cast（@AN_INT as int）FROM RDB $ DATABASE 。 Else Firebird不知道参数类型是什么（即使它是在C＃代码中指定的）。

Your first query needs to be SELECT cast(@AN_INT as int) FROM RDB$DATABASE. Else Firebird doesn't know what the parameter type is (even if it's specified in C# code).

您可以尝试直接在Firebird中运行这段代码发动机本身的限制。

You can try to run this piece of code directly in Firebird to see the limitation of engine itself.

execute block
as
begin
    execute statement ('select :foobar from rdb$database')(foobar := 10);
end