SQL & PL/SQL

Hi,

I'm a beginner on the Oracle technology and I'm trying add a step on my logon trigger that avoids that the same user connects twice to the database using PL/SQL Developer.

Here what I'm doing:

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VUSER := UPPER(SYS_CONTEXT('USERENV', 'SESSION_USER'))

VPROGRAM := UPPER(SYS_CONTEXT('USERENV', 'MODULE'))
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SELECT COUNT(*) INTO N_SESSION
FROM V$SESSION
WHERE USERNAME = UPPER(SYS_CONTEXT('USERENV', 'SESSION_USER'));

IF VUSER NOT IN ('SYS','SYSTEM') AND N_SESSION >= 2 AND VPROGRAM LIKE 'PLSQLDEV%' THEN
RAISE_APPLICATION_ERROR(-20003,
'Access to database ' ||
UPPER(SYS_CONTEXT('USERENV', 'DB_NAME')) ||
' denied for this application');
END IF;
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For some reason, it's not working.

Do you guys know what I should do?

Thanks