Updated at: May 11, 2017
mysql> create table cnt_test (id tinyint);
Query OK, 0 rows affected (0.04 sec)
mysql> insert cnt_test values (1),(2),(NULL),(4);
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from cnt_test;
+------+
| id |
+------+
| 1 |
| 2 |
| NULL |
| 4 |
+------+
4 rows in set (0.00 sec)
mysql> select count(*) from cnt_test;
+----------+
| count(*) |
+----------+
| 4 |
+----------+
1 row in set (0.00 sec)
mysql> select count(id) from cnt_test;
+-----------+
| count(id) |
+-----------+
| 3 |
+-----------+
1 row in set (0.00 sec)
mysql> select count(1) from cnt_test;
+----------+
| count(1) |
+----------+
| 4 |
+----------+
1 row in set (0.00 sec)