Conversion of String with Abbreviated Timezone to Timestamp

Question

I have a timestamp stored as varchar2 in May 29 14:12:56 PDT 2015 format. I want to convert this into timestamp with time zone data type.

If I

Answer 1

Actually your query should raise error ORA-01857: not a valid time zone or ORA-01882: timezone region not found

PDT is not a valid time zone region, i.e. it is ambiguous. Run this query to get different meanings of PDT:

SELECT tzabbrev, TZ_OFFSET(tzname), tzname
FROM v$timezone_names 
WHERE tzabbrev = 'PDT'
ORDER BY 2;

TZABBREV    TZ_OFFSET(TZNAME)   TZNAME
PDT -06:00  America/Inuvik
PDT -07:00  US/Pacific-New
PDT -07:00  America/Ensenada
PDT -07:00  America/Dawson
PDT -07:00  America/Dawson_Creek
PDT -07:00  America/Los_Angeles
PDT -07:00  America/Tijuana
PDT -07:00  America/Vancouver
PDT -07:00  America/Whitehorse
PDT -07:00  Canada/Pacific
PDT -07:00  Canada/Yukon
PDT -07:00  Mexico/BajaNorte
PDT -07:00  PST
PDT -07:00  PST8PDT
PDT -07:00  US/Pacific
PDT -08:00  America/Juneau

You have to use PST as time zone region. Daylight saving settings are then determined from given day:

SELECT 
    TO_TIMESTAMP_TZ('Jan 29 14:12:56 PST 2015','Mon dd hh24:mi:ss TZR YYYY') dt_ts_winter,
    TO_TIMESTAMP_TZ('Jun 29 14:12:56 PST 2015','Mon dd hh24:mi:ss TZR YYYY') dt_ts_summer 
FROM dual;

DT_TS_WINTER                            DT_TS_SUMMER
2015-01-29 14:12:56.000000000 -08:00    2015-06-29 14:12:56.000000000 -07:00

Since your values are stored as VARCHAR2 (now you know why you should not do it like this) you can change it with REGEXP_REPLACE(dt_string, 'PDT', 'PST')