Aggregation and sequencing of SQL basics

Aggregate functions are functions that are used to sum, average, and maximum minimum values.

Commonly used are count, SUM, MAX, MIN, AVG.

Count ()

The parameter is a column name, or you can use * to represent all columns.

The default * will count all rows of data, and if you want to filter out null rows, specify a specific column name.

Filter Blank lines:

Mysql> SELECT * FROM Employees where ' to_date ' is null; Empty Set (0.00 sec)

Aggregation and sequencing of SQL basics