The
In your example SQL,
It is like getting the results of a
It is useful when you use the
Read the linked AskTom article for further details.
Hope this helps.
http://stackoverflow.com/questions/561836/oracle-partition-by-keyword
PARTITION BY clause sets the range of records that will be used for each "GROUP" within the OVER clause.In your example SQL,
DEPT_COUNT will return the number of employees within that department for every employee record. (It is as if your de-nomalising the emp table; you still return every record in the emp table.)emp_no dept_no DEPT_COUNT1 10 3
2 10 3
3 10 3 <- three because there are three "dept_no = 10" records4 20 2
5 20 2 <- two because there are two "dept_no = 20" recordsstate) then you could count how many departments in that State.It is like getting the results of a
GROUP BY (SUM, AVG, etc.) without the aggregation of the result set.It is useful when you use the
LAST OVER or MIN OVER
functions to get, for example, the lowest and highest salary in the
department and then use that in a calulation against this records salary
without a sub select. It is also much faster.Read the linked AskTom article for further details.
Hope this helps.
http://stackoverflow.com/questions/561836/oracle-partition-by-keyword
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