What is the purpose of the "GROUP BY" clause in a MySQL query and how does it affect the results?

The "GROUP BY" clause in a MySQL query is used to group rows that have the same values into summary rows. It is often used with aggregate functions like COUNT, SUM, AVG, etc. to perform calculations on the grouped data. This clause affects the results by organizing the data into groups based on the specified column(s) and allowing you to perform aggregate functions on those groups. 

$query = "SELECT column1, COUNT(column2) 
          FROM table_name 
          GROUP BY column1";
$result = mysqli_query($connection, $query);

// Loop through the results
while($row = mysqli_fetch_assoc($result)) {
    echo $row['column1'] . ": " . $row['COUNT(column2)'] . "<br>";
}

Keywords

MySQL GROUP BY query results aggregation

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