Database aggregation functions

Aggregation functionsSQL Server provides a series of aggregate functions. These functions describe the data stored in the database as a whole rather than a row of orphaned records, which can be used to summarize data sets or to calculate averages.

As An example ,Query the category of majors from the S tableThe s table is as follows:

SQL statements and Results

Note: Use the DISTINCT keyword to handle different values in a column or an expression
when the DISTINCT keyword is not applied, the results are as follows

Analysis: Statistics is the number of data items in the Professional column, and does not remove duplicate values
It is also important to note that aggregate functions are in the database tables and not in the result set.

Database aggregation functions