sql average

1/*COUNT(column_name) will return the number of rows from the column 
2that are not NULL*/
3SELECT COUNT(column_name)
4FROM table_name;
5
6/*COUNT(*) will return the number of rows from the table*/
7SELECT COUNT(*)
8FROM table_name;

1SELECT AVG(column_name)
2FROM table_name
3WHERE condition;

1SELECT FIRST_NAME FROM EMPLOYEES
2WHERE SALARY = (SELECT AVG(SALARY) FROM EMPLOYEES);

1/*AVG() is an aggregate function that returns the 
2   average value for a numeric column*/
3SELECT AVG(column_name)
4FROM table_name;

1SELECT student_name, avg(notes) FROM student_notes GROUP BY student_name;