The current AD 6.20-based syntax related to the default_schema attribute is as follows.
SHOW
SHOW default_schema;
Shows the current default schema which is searched when an object (table, view, and so on) is referenced by a name with no schema component.
ALTER USER
ALTER USER username SET default_schema { TO | = } schemaname;
This sets the default schema of the user. When the user subsequently starts a new session, the specified schema is used as its default.
SET
SET [ LOCAL | TRANSACTION | SESSION ] default_schema { TO | = } schemaname;
This specifies the default schema to search when an object (table, view, and so on) is referenced by a name with no schema component. Pass the session qualifier to limit the use of the default schema to the current session. Pass the local or transaction qualifier to limit the use of the default schema to the current transaction. If no qualifier is passed, the default_schema applies to the current transaction.