Aggregation and grouping query technology in PHP

PHP language is a programming language widely used in Web development. It has powerful data processing capabilities. In PHP development, aggregation and group query are two very commonly used technologies. This article will introduce these two technologies in detail.

1. Aggregation query

Aggregation query aggregates multiple records in the table into a single result, usually a value or a set of values. Aggregation queries can perform statistics, calculations, filtering and other operations on data to finally get the results we want.

In PHP, we can use SQL statements to perform aggregate queries. Commonly used aggregate functions include the following:

1. COUNT(): counts the number of records.
2. SUM(): Calculate the sum.
3. AVG(): Calculate the average.
4. MAX(): Find the maximum value.
5. MIN(): Find the minimum value.

The following is a sample code that demonstrates how to use an aggregate query to count the number of records in a table:

// 连接到数据库
$conn = mysqli_connect("localhost", "username", "password");

// 选择数据库
mysqli_select_db($conn, "mydb");

// 执行查询
$result = mysqli_query($conn, "SELECT COUNT(*) FROM mytable");

// 获取结果
$row = mysqli_fetch_row($result);
$count = $row[0];

// 关闭连接
mysqli_close($conn);

In the above code, we use the COUNT() function to Count the number of records in the table and obtain the query results through the mysqli_fetch_row() function. It is important to note that we must first connect to the database and select the correct database before we can execute the query.

2. Group query

Group query refers to classifying data according to certain rules and dividing it into multiple groups. Each group can be aggregated and queried. By grouping queries, we can analyze the data in more detail and get more meaningful results.

In PHP, we can also use SQL statements to perform group queries. The commonly used GROUP BY clause can group data according to specified columns. The following is a sample code that demonstrates how to use the GROUP BY clause to perform a group query on a table:

// 连接到数据库
$conn = mysqli_connect("localhost", "username", "password");

// 选择数据库
mysqli_select_db($conn, "mydb");

// 执行查询
$result = mysqli_query($conn, "SELECT category, AVG(price) FROM mytable GROUP BY category");

// 获取结果
while ($row = mysqli_fetch_assoc($result)) {
    echo "Category: " . $row['category'] . ", AVG price: " . $row['AVG(price)'] . "
";
}

// 关闭连接
mysqli_close($conn);

In the above code, we use the GROUP BY clause to perform a group query based on the category of the product. , and calculated the average price for each category. Through the mysqli_fetch_assoc() function, we can obtain each row of records in the query results.

Summary

In PHP development, aggregation and grouping queries are very common technologies. Through aggregation queries, we can perform statistics, calculations, filtering and other operations on the data to get the results we want; through group queries, we can analyze the data in more detail and get more meaningful results. When using aggregation and grouping queries, we need to pay attention to details such as connecting to the database, selecting the database, and correctly writing SQL statements.

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