MySql重叠日期无法正确完成

Question

I am trying to make a query with overlapping dates. My tabel look like this'

Agenda ID   DateStart               DateEnd
-------------------------------------------------------
1           2012-04-02 08:00:00     2012-04-02 11:30:00
2           2012-04-02 10:00:00     2012-04-02 13:00:00
3           2012-04-02 12:00:00     2012-04-02 15:00:00

This data is for planning activities. You can't plan a activity if the time overlaps. In this case all the times overlap. But he compares it to the one you planned earlier. Say I planned ID 1, so I can't plan ID 2, But I can plan ID 3.

How Can I write A query with php to select the items that overlap. Thank you very much

SELECT
   agenda.DateStart,
   agenda.DateEnd,
   agenda.AgendaID
FROM
   AGENDA
WHERE
   ????
   AND
   ????

Answer 1

select a.DateStart, a.DateEnd, a.AgendaId, b.DateStart, b.DateEnd, b.AgendaId
from agenda a, agenda b
where 
a.AgendaId <> b.AgendaId
and b.DateStart>= a.DateStart and
b.DateStart<= a.DateEnd