secuencia de caída de Oracle si existe

DECLARE
    s_exist NUMBER(1);
BEGIN
    SELECT CASE WHEN exists(SELECT * FROM ALL_SEQUENCES 
                           WHERE SEQUENCE_NAME = 'seq_name') THEN 1
       	ELSE 0 
    END INTO s_exist FROM DUAL;
    IF s_exist = 1 THEN
        EXECUTE IMMEDIATE 'DROP SEQUENCE seq_name';
    END IF;
END;
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