We talked about SQL in the last article
单行函数. In fact, there is another class of SQL functions called SQL functions聚合（或聚集、分组）函数, which are functions that summarize a set of data. The input is a set of data, and the output is a single value. Next, let's take a look at what is an aggregate function and the classification of aggregate functions
1. Introduction to aggregate functions
1.1 What is an aggregate function?
聚合函数Acts on a set of data and returns a value for a set of data.
aggregate function type
- AVG()
- SUM()
- MAX()
- MIN()