--windows functions are really powerful and are somewhat like a group by - except they don't roll everything up into 1 row when grouping. --windows functions allow us to look at a partition or a group ...

Two clauses driving this: OVER () - marks it as a window function PARTITION BY - divides rows into groups, aggregation runs independently per group Then I learned ROW_NUMBER (), RANK () and DENSE_RANK ...

The primary key index is also updated to record the new location (data file and row number) of the changed data row. During data reading, because historical duplicate records in various data files ...

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