Alibaba Tianchi SQL training camp learning notes 5

This note is about Alibaba cloud Tianchi Longzhu project SQL Learning content of training camp , Link to ：https://tianchi.aliyun.com/specials/promotion/aicampsql;

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Window function

The window function is also called OLAP function .OLAP yes OnLine AnalyticalProcessing For short , It means real-time analysis and processing of database data .
For the sake of understanding , It is called window function . The conventional SELECT Statements are used to query the whole table , The window function allows us to selectively summarize some data 、 Calculate and sort .
General form of window function ：
< Window function > OVER ([PARTITION BY < Name >]
ORDER BY < Column names for sorting >)
[] Can be omitted .
The key of window function is to understand the keyword PARTITON BY and ORDER BY ***** The role of .
PARTITON BY Is used to group , That is, select which window you want to see , Be similar to GROUP BY Clause grouping function , however PARTITION BY Clause does not have GROUP BY The summary function of clause , It does not change the number of rows recorded in the original table .
ORDER BY It's used to sort , That is, in the decision window , According to that rule ( Field ) To sort .
For the most part , Window functions can be divided into two categories .
One is take SUM、MAX、MIN Aggregate functions such as are used in window functions
Two is RANK、DENSE_RANK And other special window functions for sorting
author ： Chumei ChuM

Game programming , A game development favorite ~

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