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Thread: strange java query behaviour

strange java query behaviour

From
Szymon Guz
Date:
Hi,
I've got a quite strange situation. Below is a simple test

    @Test
    public void test() throws SQLException {

        String query1 = "SELECT * FROM information_schema.schemata WHERE schema_name = ?";
        String query2 = "SELECT * FROM pg_catalog.pg_namespace where nspname = ?";

        check(query1, "1", "public");
        check(query2, "2", "public");

    }

    private void check(final String query, final String info, final String param) throws SQLException {
        PreparedStatement stmt = connection.prepareStatement(query);
        stmt.setString(1, param);
        ResultSet schemas = stmt.executeQuery();
        boolean exists = schemas.next();
        System.out.println(info + " : " + exists);
    }

The output is:

1 : false
2 : true

When I query the database using psql, both queries return sensible data (even when I prepare statements in postgres).

I'd like to use information_schema rather than using pg_catalog.

ENV:

Ubuntu 11.10
PostgreSQL 9.0.4 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
java version "1.6.0_26"
Java(TM) SE Runtime Environment (build 1.6.0_26-b03)
Java HotSpot(TM) 64-Bit Server VM (build 20.1-b02, mixed mode)
9.0-801.jdbc4


regards
Szymon


Re: strange java query behaviour

From
Marti Raudsepp
Date:
On Mon, Oct 24, 2011 at 23:23, Szymon Guz <mabewlun@gmail.com> wrote:
> String query1 = "SELECT * FROM information_schema.schemata WHERE schema_name = ?";

> When I query the database using psql, both queries return sensible data
> (even when I prepare statements in postgres).
> I'd like to use information_schema rather than using pg_catalog.

The documentation says: The view schemata contains all schemas in the
current database that are owned by a currently enabled role.

In other words: this view only displays schemas that are *owned* by
your user, or roles that your current user inherits from (superuser
sees everything of course). Sadly it doesn't list visible/accessible
schemas.

I think this is pretty surprising; not sure if it's just bad legacy or
if there is some good reason for this behavior. I couldn't find any
justification in the source code.

I think we should add a TODO item for fixing this?

Regards,
Marti

Re: strange java query behaviour

From
Szymon Guz
Date:


On 25 October 2011 17:04, Marti Raudsepp <marti@juffo.org> wrote:
On Mon, Oct 24, 2011 at 23:23, Szymon Guz <mabewlun@gmail.com> wrote:
> String query1 = "SELECT * FROM information_schema.schemata WHERE schema_name = ?";

> When I query the database using psql, both queries return sensible data
> (even when I prepare statements in postgres).
> I'd like to use information_schema rather than using pg_catalog.

The documentation says: The view schemata contains all schemas in the
current database that are owned by a currently enabled role.

In other words: this view only displays schemas that are *owned* by
your user, or roles that your current user inherits from (superuser
sees everything of course). Sadly it doesn't list visible/accessible
schemas.

I think this is pretty surprising; not sure if it's just bad legacy or
if there is some good reason for this behavior. I couldn't find any
justification in the source code.

I think we should add a TODO item for fixing this?

Regards,
Marti

Hi,
thanks for the answer. I was really my fault: I've been using user test in the java test and postgres user in psql. I've changed the user to 
postgres in java and results are OK now.

regards
Szymon

Re: strange java query behaviour

From
Tom Lane
Date:
Marti Raudsepp <marti@juffo.org> writes:
> The documentation says: The view schemata contains all schemas in the
> current database that are owned by a currently enabled role.

> In other words: this view only displays schemas that are *owned* by
> your user, or roles that your current user inherits from (superuser
> sees everything of course). Sadly it doesn't list visible/accessible
> schemas.

> I think this is pretty surprising; not sure if it's just bad legacy or
> if there is some good reason for this behavior. I couldn't find any
> justification in the source code.

The justification is that the SQL standard requires the view to act that
way.

         20.46  SCHEMATA view

         Function

         Identify the schemata in a catalog that are owned by a given user.

         Definition

         CREATE VIEW SCHEMATA AS
             SELECT CATALOG_NAME, SCHEMA_NAME, SCHEMA_OWNER,
                    DEFAULT_CHARACTER_SET_CATALOG, DEFAULT_CHARACTER_SET_
         SCHEMA,
                    DEFAULT_CHARACTER_SET_NAME, SQL_PATH
             FROM DEFINITION_SCHEMA.SCHEMATA

             WHERE ( SCHEMA_OWNER = CURRENT_USER
                   OR
                     SCHEMA_OWNER IN
                     ( SELECT ROLE_NAME
                       FROM ENABLED_ROLES ) )
               AND
                   CATALOG_NAME
                 = ( SELECT CATALOG_NAME
                     FROM INFORMATION_SCHEMA_CATALOG_NAME );

         GRANT SELECT ON TABLE SCHEMATA
             TO PUBLIC WITH GRANT OPTION;

> I think we should add a TODO item for fixing this?

Waste of breath.  You could try lobbying the SQL committee to change the
standard, perhaps.

            regards, tom lane