Query to retrieve date depending on specific date

Question

hi all,
i have a question regarding dates.
ihave a table with following data
with table1 as
  select 123 id, 'text' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 111 id, 'text2' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 222 id, 'text3' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 333 id, 'text4' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 444 id, 'text5' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual union all
  select 555 id, 'text6' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual union all
  select 666 id, 'text7' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual union all
  select 777 id, 'text8' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual
)i am creating a procedure that will insert data into a table and this procedure will run every day.
so for example, if procedure runs today, then it will check today's date against table1 and see we have
4 rows for 9/16/2010 and insert into a table. then tomorrow 9/17/2010 it will see if there is a 9/17/2010 data.
since there is no data, then the 4 rows with 9/16/2010 should be pick up and inserted with 9/17/2010 date.
now lets say that today is 9/20/2010 then the query should pick up 9/20/2010 data set.
for 9/21/2010 the same data set for 9/20/2010 should be pick since that is the latest date less than or equal to 9/21/2010
here is sample output.
lets say we run query today. then output should be
id     txt       date1
================================
123     text     09.16.2010  
111     text2     09.16.2010
222     text3     09.16.2010
333     text4     09.16.2010 now lets say today is 9/17/2010 then query will look at table for the 9/17/2010, since it is not found
it will be pick the latest less than or equal to 9/17/2010
output should be
id     txt       date1
================================
123     text     09.17.2010  
111     text2     09.17.2010
222     text3     09.17.2010
333     text4     09.17.2010 now lets say that today is 9/20/2010, the query will look at the table for date 9/20/2010, it found there there is an entry and will pick up that data set.
so output should be
444     text5     09.20.2010
555     text6     09.20.2010
666     text7     09.20.2010
777     text8     09.20.2010if you run for 9/21/2010 , query should pick up latest date less or equal to 9/21/2010 which is 9/20/2010 so output should be
444     text5     09.21.2010
555     text6     09.21.2010
666     text7     09.21.2010
777     text8     09.21.2010can someone help write a query that given a date can retrieve output above? thanks

Answer 1

with table1 as
  select 123 id, 'text' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 111 id, 'text2' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 222 id, 'text3' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 333 id, 'text4' txt, to_date('9/16/2010','mm/dd/yyyy') date1 from dual union all
  select 444 id, 'text5' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual union all
  select 555 id, 'text6' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual union all
  select 666 id, 'text7' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual union all
  select 777 id, 'text8' txt, to_date('9/20/2010','mm/dd/yyyy') date1 from dual
/* substitute trunc(sysdate) with your parameter */
select t.id, t.txt, trunc(sysdate)  as date1 from table1 t
where t.date1=(select max(t2.date1) from table1 t2 where t2.date1 <= trunc(sysdate) )