windows functions OVER, PARTITION

what are uses of Windows functions like

OVER(), PARTITION etc.

is it supported in all the databases?

what are other windows functions are there?
why they called windows functions

please advise
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gudii9Asked:
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Scott PletcherSenior DBACommented:
All major relational dbs will support them, since they are now part of the ANSI standard.

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kaufmed   ( ⚆ _ ⚆ )I asked the operating system what I could do to become a better programmer. It said, "Let me give you some pointers."Commented:
*Window functions

"Windows functions" sounds like you're asking about the operating system  = )
David Johnson, CD, MVPRetiredCommented:
Window functions operate on a set of rows and return a single value for each row from the underlying query. The term window describes the set of rows on which the function operates. A window function uses values from the rows in a window to calculate the returned values.
https://drill.apache.org/docs/sql-window-functions-introduction/
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slightwv (䄆 Netminder) Commented:
Check in some of the online docs:
https://docs.oracle.com/cd/B19306_01/server.102/b14223/analysis.htm#i1006709

Windowing Aggregate Functions

Windowing functions can be used to compute cumulative, moving, and centered aggregates. They return a value for each row in the table, which depends on other rows in the corresponding window. With windowing aggregate functions, you can calculate moving and cumulative versions of SUM, AVERAGE, COUNT, MAX, MIN, and many more functions. They can be used only in the SELECT and ORDER BY clauses of the query. Windowing aggregate functions include the convenient FIRST_VALUE, which returns the first value in the window; and LAST_VALUE, which returns the last value in the window. These functions provide access to more than one row of a table without a self-join.

In a nut-shell:  They allow you to operate on a "window" (subset of rows) over the entire result set.
gudii9Author Commented:
when we use

RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW


please advise
gudii9Author Commented:
how ORDER BY inside OVER() different from PARTITION inside OVER()
slightwv (䄆 Netminder) Commented:
>>when we use RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW

Easy and just like several of your questions:  Use it when you need it.

There are several other RANGE options that are allowed.  Once you understand them and what they do, you'll know when you need them.

For example, I used them in a recent question:
https://www.experts-exchange.com/questions/29104922/Data-Validation.html

I needed to fill in gaps that were null with a previous value.

I needed to repeat the id for null values on what the previous value was so instead of:
10,null,20,null,null,30

I needed:
10,10,20,20,20,30

>>how ORDER BY inside OVER() different from PARTITION inside OVER()

PARTITION BY is similar to a GROUP BY in a regular query.  It is the grouping for the window.  I hope ORDER BY is self explanatory.  It sets the order for the objects inside the window for the partition (group).

Similar to a regular query: select ...from ... where  group by some_column order by some_other_column;
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