You can see the Count command before using GROUP BY command here. GROUP BY
command will create groups in the field name specified and will count the number
of records in the groups. This is very useful command.
We can also use WHERE command along with GROUP BY command in Mysql tables.
SELECT count(*) as total_records, class FROM `student` group by class
This will display the total records in each class. Like this
total_records
class
1
Eight
3
Five
9
Four
2
Nine
10
Seven
7
Six
3
Three
Let us try to get the total number of girls records in each class by using GROUP BY query. Here we want to filter our query for only girls so we have to use one WHERE clause to restrict the records using the sex field. Here is the query.
SELECT class,count( * ) AS total_records FROM `student` WHERE sex='female' GROUP BY class
We can find out duplicate records in a table by using group by command. We will create another table student2_1 by using same data and by adding some duplicate records. Here is the query
SELECT name, COUNT(id) AS no from student2_1 group by name having no > 1
Output is here .
name
no
Arnold
2
Tade Row
3
You can download the SQL dump of this stduent2_1 table with added duplicate data at the end of this page.
Here is a sample code to understand how to use group by query using PHP script and PDO.
require "../config.php"; // Database connection
///////////////////////////
$sql="SELECT count(*) as total_records, class FROM `student` group by class ";
echo "<table>";
foreach ($dbo->query($sql) as $row) {
echo "<tr ><td>$row[class]</td><td>$row[total_records]</td></tr>";
}
echo "</table>";
