Re: stringtype=unspecified is null check problem

The problem is about generic queries, where the user writes something like:

… where (:SEARCH is null or table.id<http://or table.id> = :SEARCH)

The parameters are replaced by ? and the value is bound to the statement.

The stringtype=unspecified solves the problem for table.id<http://for table.id> = :SEARCH, but causes the problem for :SEARCH is null.

So with stringtype=VARCHAR :SEARCH is null is working, but table.id<http://but table.id> = :SEARCH fails.

A developer is of course able to write a cast(? as varchar), normal users maybe not, and it breaks database independency.

The database parses the statement and knowns therefore the use case. It would be the central place. Maybe there is also a solution in the jdbc driver?

Statement parsing, is complex, so it would be fine, to find any solution without parsing the statement.

Am 10. Jan. 2023, um 18:44, "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com<mailto:david(dot)g(dot)johnston(at)gmail(dot)com>> schrieb:
On Tuesday, January 10, 2023, Martin Handsteiner <martin(dot)handsteiner(at)sibvisions(dot)com<mailto:martin(dot)handsteiner(at)sibvisions(dot)com>> wrote:
If a bind parameter is checked for null, ERROR: could not determine data type of parameter $1 occurs.
Simple testcase:
Connection conn = DriverManager.getConnection("jdbc:postgresql://192.168.1.201:5432/testdb?stringtype=unspecified<http://192.168.1.201:5432/testdb?stringtype=unspecified>", "test", "test");
PreparedStatement stat = conn.prepareStatement("select 1 where ? is null");
stat.setNull(1, Types.VARCHAR);
stat.executeQuery();
-> Exception

For checking the parameter for null, the data type should not be relevant. At least TEXT or VARCHAR could be implicitly used.

There is a mailing post, that says, that stat.setNull(1, Types.VARCHAR); would strict set the value as VARCHAR.
https://www.postgresql.org/message-id/Pine.BSO.4.64.0702141439480.24142%40leary.csoft.net
But this seams not to happen in my case.

I have also testet to bind the value with:
stat.setNull(1, Types.NULL); or stat.setNull(1, Types.OTHER); or stat.setString(1, null);
Nothing works in this case.

As far as I understand, the jdbc driver sends the value without type information to the database. The database throws the exception.
So maybe this is a database problem.
The database can assume, that in case of ? is null it doesn't matter, which type the sent null is. So even a UNKOWN null is null or not null.

Strange is, that the following statement will work. So in this case null is unknown, but mapped.
conn.prepareStatement("select 1 where coalesce(?, null) is null");

This is indeed how all of this works in the current design. I suggest you add a cast to the input parameter in the query. Or choose a different value for stringtype…

David J.