What are the windowing functions?

Window functions include ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE(n), LAG(column, offset), LEAD(column, offset) and SUM(), AVG(), MIN (), MAX(). Detailed introduction: 1. ROW_NUMBER(), usually used to sort or page the result set; 2. RANK(), calculate the ranking of each row; 3. DENSE_RANK(), etc.

Window function (Window Function) is a function used in SQL to perform group calculations on query result sets. It can perform calculations on each row of query results and return results relevant to the current row. The following are some common windowing functions:

1. ROW_NUMBER(): Assigns a unique integer value to each row, usually used to sort or page the result set.

2. RANK(): Calculate the ranking of each row. If there are the same values, the same ranking will be skipped and the same ranking value will be generated.

3. DENSE_RANK(): Similar to the RANK() function, but it will not skip the same ranking, but assign ranking values in consecutive order.

4. NTILE(n): Divide the result set into n equal-sized buckets and assign a corresponding bucket number to each row.

5. LAG(column, offset): Get the value of a column in the row whose offset is offset before the current row. Can be used to calculate the difference between the current row and the previous row.

6. LEAD(column, offset): Get the value of a column in the row with offset after the current row. Can be used to calculate the difference between the current row and the next row.

7. SUM(), AVG(), MIN(), MAX(): These aggregate functions can be used with windowing functions to calculate summary values for each grouping rather than for the entire result set.

These are just some common examples of windowing functions. In fact, there are many other windowing functions that can be used according to specific needs. When using windowing functions, you need to understand the specific syntax and supported functions of the database system, and select the appropriate windowing function based on query requirements to achieve the required calculations and analysis.

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