sql - Oracle query - without temporary table -

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i'm new oracle , need query. have table data samples /records like:

name | datetime -----------    | 20140414 10:00    | 20140414 10:30    | 20140414 11:00 b    | 20140414 11:30 b    | 20140414 12:00    | 20140414 12:30    | 20140414 13:00    | 20140414 13:30

and need "group"/get informations form:

name | datetime_from  | datetime_to ----------------------------------    | 20140414 10:00 | 20140414 11:00 b    | 20140414 11:30 | 20140414 12:00    | 20140414 12:30 | 20140414 13:30

i couldnt find solution query similar this. please me?

note: dont want use temporary tables.

thanks, pavel

you need find periods values same. easiest way in oracle use lag() function, logic, , aggregation:

select name, min(datetime), max(datetime) (select t.*,              sum(case when name <> prevname 1 else 0 end) on (order datetime) cnt       (select t.*, lag(name) on (order datetime) prevname             table t            ) t      ) t group name, cnt;

what count, given value of datetime, number of times name has switched on or before datetime. identifies periods of "constancy", used aggregation.


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