count(1) in sql code example

Example 1: sql count

/*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;

Example 2: count occurrences sql

SELECT age, count(age) 
  FROM Students 
 GROUP by age