/*COUNT(column_name) will return the number of rows from the column
that are not NULL*/
SELECT COUNT(column_name)
FROM table_name;
/*COUNT(*) will return the number of rows from the table*/
SELECT COUNT(*)
FROM table_name;SELECT FIRST_NAME FROM EMPLOYEES
WHERE SALARY = (SELECT AVG(SALARY) FROM EMPLOYEES);SELECT avg(count)
FROM
(
SELECT COUNT (*) AS Count
FROM Table T
WHERE T.Update_time =
(SELECT MAX (B.Update_time )
FROM Table B
WHERE (B.Id = T.Id))
GROUP BY T.Grouping
) as countsSELECT FIRST_NAME FROM EMPLOYEES
WHERE SALARY > (SELECT AVG(SALARY) FROM EMPLOYEES);SELECT first_name, salary FROM employees
WHERE salary <= (SELECT AVG(salary) FROM employees);