Conversion from Sybase ASA - Mailing list pgsql-sql

select 'T' as src,(if tbon is null or tbon < '1900/12/12' or tbon > '1900/9/30' then 'U' else 'P' endif) as pres from ftrans

this returns two columns: src = 'T' and pres which has either the value 'U' or 'P'

how would I express this in postgresql?

thanks

Richard