Difference between count(*) and count(columnName) in MySQL?
The count(*) returns all rows whether column contains null value or not while count(columnName) returns the number of rows except null rows.
Let us first create a table.
Following is the query
mysql> create table ifNotNullDemo
-> (
-> Name varchar(20)
-> );
Query OK, 0 rows affected (0.54 sec)
Following is the query to insert some records in the table using insert command:
mysql> insert into ifNotNullDemo values('Chris');
Query OK, 1 row affected (0.15 sec)
mysql> insert into ifNotNullDemo values('');
Query OK, 1 row affected (0.13 sec)
mysql> insert into ifNotNullDemo values('Robert');
Query OK, 1 row affected (0.24 sec)
mysql> insert into ifNotNullDemo values(null);
Query OK, 1 row affected (0.30 sec)
mysql> insert into ifNotNullDemo values(0);
Query OK, 1 row affected (0.16 sec)Following is the query to display all records from the table using select statement:
mysql> select *from ifNotNullDemo;
This will produce the following output
+--------+
| Name |
+--------+
| Chris |
| |
| Robert |
| NULL |
| 0 |
+--------+
5 rows in set (0.00 sec)
Case 1: Following is the demo of count(*) that includes null as well in the count:
mysql> select count(*) from ifNotNullDemo;
This will produce the following output
+----------+
| count(*) |
+----------+
| 5 |
+----------+
1 row in set (0.02 sec)
Case 2: Following is the query for count(columnName).
mysql> select count(Name) from ifNotNullDemo;
This will produce the following output
+-------------+
| count(Name) |
+-------------+
| 4 |
+-------------+
1 row in set (0.00 sec)
Published on 17-Apr-2019 14:38:12
