sql--join query, aggregate function, window function

Connection Query

• Inner JOIN, with the most, representing more than one table one by one corresponding

Aggregation functions

• Manipulating row data, merging
• Sum, AVG, COUNT, Max, min

Open Window function

• Distributes the merged data to each row of the original table, which is the equivalent of a column that may be the sum of sums, or the value of the AVG average
• can also be used with the ranking function

Grouping functions

• To group A column, that is, to compress the data
• Grouping keywords are often used in conjunction with aggregate functions to calculate the combined values of each group
• After group BY, if it is multiple, the values of the multiple columns identified are divided into a single group

sql--join query, aggregate function, window function