Counting presence of a NOT NULL value in MySQL

MySQLMySQLi Database

To count presence of a NOT NULL value, use aggregate function COUNT(yourColumnName). Let us first create a table −

mysql> create table DemoTable
   (
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   NumberOfQuestion int,
   NumberOfSolution int
   );
Query OK, 0 rows affected (0.20 sec)

Insert some records in the table using insert command. Here, some of the values are NULL −

mysql> insert into DemoTable(NumberOfQuestion,NumberOfSolution) values(20,10);
Query OK, 1 row affected (0.06 sec)

mysql> insert into DemoTable(NumberOfQuestion,NumberOfSolution) values(20,2);
Query OK, 1 row affected (0.04 sec)

mysql> insert into DemoTable(NumberOfQuestion,NumberOfSolution) values(20,NULL);
Query OK, 1 row affected (0.03 sec)

mysql> insert into DemoTable(NumberOfQuestion,NumberOfSolution) values(20,NULL);
Query OK, 1 row affected (0.05 sec)

mysql> insert into DemoTable(NumberOfQuestion,NumberOfSolution) values(30,19);
Query OK, 1 row affected (0.04 sec)

mysql> insert into DemoTable(NumberOfQuestion,NumberOfSolution) values(30,1);
Query OK, 1 row affected (0.04 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+----+------------------+------------------+
| Id | NumberOfQuestion | NumberOfSolution |
+----+------------------+------------------+
| 1  | 20               | 10               |
| 2  | 20               | 2                |
| 3  | 20               | NULL             |
| 4  | 20               | NULL             |
| 5  | 30               | 19               |
| 6  | 30               | 1                |
+----+------------------+------------------+
6 rows in set (0.00 sec)

Following is the query to count presence of value. The same value should be NOT NULL i.e. NULL values won’t be counted −

mysql> SELECT NumberOfQuestion, COUNT(NumberOfSolution) as NumberOfRows FROM DemoTable GROUP BY NumberOfQuestion;

This will produce the following output −

+------------------+--------------+
| NumberOfQuestion | NumberOfRows |
+------------------+--------------+
| 20               | 2            |
| 30               | 2            |
+------------------+--------------+
2 rows in set (0.00 sec)
raja
Published on 20-May-2019 12:26:41
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