Convert sysdate to BST(British Summer Time) - sql

Question

I have a Java api which gets the data from oracle database which is in ET timezone. I want to query that table using sysdate on 2 columns but the sysdate should be picked as current BST date value not as ET date value.
select * from customers where sysdate between mem_registered_date and mem_deregistered_date;
How this can be done? please help

Answer 1

The simplest way to convert between time zones is to use a data type that understands time zones, a TIMESTAMP. Then when you've converted to the time zone you want then CAST it back to a DATE data type:
SELECT *
FROM customers
WHERE CAST( SYSTIMESTAMP AT TIME ZONE 'Europe/London' AS DATE )
BETWEEN mem_registered_date AND mem_deregistered_date;
I'm assuming that you want the current time in the United Kingdom (BST in summer and GMT in winter), if you want the time zone UTC+1 then use:
CAST( SYSTIMESTAMP AT TIME ZONE '+01:00' AS DATE )

Answer 2

If querying a column with a date-only value, without any time-of-day nor any time zone, that is, a column of a type akin to the SQL-standard DATE type, then use Java class LocalDate.
Generally best to use half-open definition of a span of time, where the beginning is inclusive while the ending is exclusive. This allows spans to nearly abut one another without gaps or overlap. So never use the SQL command BETWEEN for date-time ranges, as it is fully-closed (both beginning and ending are inclusive).
Get today’s date as seen in the wall-clock time used by the people of a particular region (a time zone).
BST is not a real time zone. For British time, use Europe/London.
ZoneId z = ZoneId.of( "Europe/London" ) ;
LocalDate today = LocalDate.now( z ) ;
The SQL will look something like this:
SELECT *
FROM event_
WHERE ? >= start_
AND ? < end_
;
Fill in the placeholders.
myPreparedStatement.setObject( 1 , today ) ;
myPreparedStatement.setObject( 2 , today ) ;
Load the date values from database into Java.
LocalDate start = myResultSet.getObject( … , LocalDate.class ) ;
TIMESTAMP WITHOUT TIME ZONE
The misnamed DATE in the Oracle database actually represents a date with time-of-date without the context of a time zone or offset-from-UTC. As such, this type cannot represent a moment, a specific point on the timeline. It the value is noon on the 23rd of January next year, we cannot know if that is noon in Tokyo, Toulouse, or Toledo — all different moments several hours apart. This DATE type is akin to the SQL-standard type TIMESTAMP WITHOUT TIME ZONE.
So for this data type, your question asking about time zones makes no sense. Apple and oranges. Involving time zones means you are tracking moments, specific points on the timeline. But the Oracle DATE cannot represent moments as discussed above.
To track moments, your should be using a column of a type akin to the SQL-standard TIMESTAMP WITH TIME ZONE.