Change all column units from byte to char

For 2: This will produce code to update all BYTE columns to CHAR

BEGIN
    FOR x in (SELECT * FROM user_tab_columns WHERE data_type LIKE 'VARCHAR%' and CHAR_USED = 'B')
    LOOP
        DBMS_OUTPUT.PUT_LINE('ALTER TABLE '||x.table_name||' MODIFY '||x.column_name||' '||x.data_type||'('||x.data_length||' CHAR)');
    END LOOP;
END;
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