oracle中的tz_offset是用来返回给定时区与标准时区(UTC universal of time Coordinate 通用时间坐标)的偏移量，其参数可以是：

1.一个合法的时区名

2.一个离UTC的标准偏移量

3.关键字SessionTimeZone或者是DB_timezone

其中合法的时区名可以从系统视图V$TimeZone_names中的列TZname中的得到：

TZNAME

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Africa/Cairo

Africa/Tripoli

America/Adak

America/Anchorage

America/Atka

America/Chicago

America/Denver

America/Detroit

America/Edmonton

America/Ensenada

America/Fort_Wayne

America/Halifax

America/Havana

America/Indiana/Indianapolis

America/Indianapolis

America/Jamaica

America/Los_Angeles

America/Manaus

America/Mazatlan

America/Mexico_City

America/Montreal

America/New_York

America/Noronha

America/Phoenix

America/Porto_Acre

America/Regina

America/Santiago

America/Sao_Paulo

America/Shiprock

America/St_Johns

America/Tijuana

America/Vancouver

America/Whitehorse

America/Winnipeg

Asia/Calcutta

Asia/Hong_Kong

Asia/Istanbul

Asia/Jerusalem

Asia/Riyadh

Asia/Seoul

Asia/Shanghai

Asia/Singapore

Asia/Taipei

Asia/Tehran

Asia/Tel_Aviv

Asia/Tokyo

Atlantic/Reykjavik

Australia/ACT

Australia/Adelaide

Australia/Brisbane

Australia/Broken_Hill

Australia/Canberra

Australia/Darwin

Australia/Hobart

Australia/LHI

Australia/Lindeman

Australia/Lord_Howe

Australia/Melbourne

Australia/NSW

Australia/North

Australia/Perth

Australia/Queensland

Australia/South

Australia/Sydney

Australia/Tasmania

Australia/Victoria

Australia/West

Australia/Yancowinna

Brazil/Acre

Brazil/DeNoronha

Brazil/East

Brazil/West

CET

CST

CST6CDT

Canada/Atlantic

Canada/Central

Canada/East-Saskatchewan

Canada/Eastern

Canada/Mountain

Canada/Newfoundland

Canada/Pacific