How to diagnose and fix the 0Z002 stacked_diagnostics_accessed_without_active_handler error code in Postgres.

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The error code 0Z002 in PostgreSQL, which corresponds to stacked_diagnostics_accessed_without_active_handler, indicates that there was an attempt to access stacked diagnostics when there was no active exception handler. This error is part of the SQLSTATE class 0Z which is for Diagnostics Exception errors.

To diagnose and fix this error, you should ensure that you are trying to access the diagnostics within an exception block that is actively handling an exception. In PL/pgSQL, which is the procedural language for PostgreSQL, this typically means that you should be within a BEGIN ... EXCEPTION ... END; block when trying to access the diagnostics.

Here’s an example of how you might encounter this error and how to fix it:

Faulty code that can cause the error:

-- Attempting to access diagnostics outside of an exception block
DO $$
BEGIN
    RAISE NOTICE 'Stacked Diagnostics: %', GET STACKED DIAGNOSTICS my_var = PG_EXCEPTION_CONTEXT;
END $$;

Corrected code with proper exception handling:

-- Correct usage of stacked diagnostics within an exception block
DO $$
DECLARE
    my_var text;
BEGIN
    -- Some code that might fail
    -- For example purposes, we'll force an error
    RAISE EXCEPTION 'This is an error!';
EXCEPTION
    WHEN OTHERS THEN
        GET STACKED DIAGNOSTICS my_var = PG_EXCEPTION_CONTEXT;
        RAISE NOTICE 'An error occurred: %', my_var;
END $$;

In the corrected code, the GET STACKED DIAGNOSTICS statement is placed inside the EXCEPTION block. This way, it only tries to access the diagnostics information when an exception has actually occurred and is being handled.

For more details on PostgreSQL error codes, you can refer to the PostgreSQL documentation.

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