Library /sys$common/syshlp/SQL$HELP72.HLB  —  SET_NATIONAL_CHARACTER_SET, Example
    Example 1: Setting the national character set for an interactive
    session

    SQL> show character sets;
    Default character set is DEC_KANJI
    National character set is DEC_MCS
    Identifier character set is SHIFT_JIS
    Literal character set is SHIFT_JIS
    Display character set is SHIFT_JIS
    SQL> set national character set 'DEC_KANJI';
    SQL> show character sets;
    Default character set is DEC_KANJI
    National character set is DEC_KANJI
    Identifier character set is SHIFT_JIS
    Literal character set is SHIFT_JIS
    Display character set is SHIFT_JIS
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