问题
I have a problem with Firebird (embedded) database. I would like to set a parameter values in the select statement. For example:
SELECT name, surname, :string AS myText
FROM myTable
where :string is a parameter.
The above code works in SQLite and the result is (when the paramenter is "abcdef"):
+------+---------+---------+
|name |surname |myText |
+------+---------+---------+
|John |Black |abcdef |
+------+---------+---------+
|Thomas|Young |abcdef |
+------+---------+---------+
|... |... |abcdef |
+------+---------+---------+
|nameX |surnameY |abcdef |
+------+---------+---------+
When I try to execute this query then I get the following message: "An error was found in the application program input parameters for the SQL statement.
Dynamic SQL Error.
SQL error code = -804.
Data type unknown.
回答1:
The problem is that Firebird needs to know the datatype of the parameter. IIRC in SQLite, everything is a string, but that is not the case in Firebird.
You will need to explicitly cast the parameter to inform Firebird about the expected type, for example:
SELECT name, surname, cast(? as varchar(100)) AS myText
FROM myTable
Where the ? is a positional parameter. Firebird doesn't have named parameters (except in procedures), but if your access library simulates named parameters, then probably the following will work as well:
SELECT name, surname, cast(:string as varchar(100)) AS myText
FROM myTable
The ability to cast parameters in the select-clause does not work in older Firebird version (I believe it was introduced in Firebird 2.5, but I'm not 100% sure).
来源：https://stackoverflow.com/questions/51526646/parameter-in-select-statements-fields-list-error-data-type-unknown