Table:

CREATE TABLE "MyTable"
(
"vusername" VARCHAR(16) COLLATE "ANSI",
"vbirthday" DATE
)

INSERT INTO "MyTable" VALUES ('Tim Young', DATE '1992-02-29')

INSERT INTO "MyTable" VALUES ('Yusuf Zorlu', DATE '1992-02-28')!

Query:

select * from (
   select
   if( vbirthday is not null and extract(year from vbirthday)>1901, cast(trim(both ' ' from cast(extract(year from current_date()) as varchar)+'-'+substring(cast(vbirthday as varchar),6,2)+'-'+substring(cast(vbirthday as varchar),9,2)) as date), null) vstart,
   if( vbirthday is not null and extract(year from vbirthday)>1901, cast(trim(both ' ' from cast(extract(year from current_date()) as varchar)+'-'+substring(cast(vbirthday as varchar),6,2)+'-'+substring(cast(vbirthday as varchar),9,2)) as date), null) vfinish,
   username
   from mytable
   where (vbirthday is not null and vbirthday>=DATE'1900-01-01')
union all
   select
   if( vbirthday is not null and extract(year from vbirthday)>1901, cast(trim(both ' ' from cast(extract(year from current_date()) as varchar)+'-'+substring(cast(vbirthday as varchar),6,2)+'-'+substring(cast(vbirthday as varchar),9,2)) as date), null) vstart,
   if( vbirthday is not null and extract(year from vbirthday)>1901, cast(trim(both ' ' from cast(extract(year from current_date()) as varchar)+'-'+substring(cast(vbirthday as varchar),6,2)+'-'+substring(cast(vbirthday as varchar),9,2)) as date), null) vfinish,
   username
   from mytable
   where (vbirthday is not null and vbirthday>=DATE'1900-01-01')
) daten