How to query the database within a period of time in php

In the process of website development, it is often necessary to query database information within a certain period of time, such as querying the registration time of a user, the ordering time of an order, or the publication time of an article. PHP provides some convenient methods to achieve this function.

1. Database query statements

First of all, we need to learn to use sql statements to query information within a certain period of time in the database. Commonly used sql statements are as follows:

• SELECT * FROM table_name WHERE datetime_column >= start_time AND datetime_column <= end_time;

Among them, table_name refers to the query we want to make The data table name, datetime_column is the column name for storing time. start_time and end_time refer to the time range we want to query. The time format here is generally YYYY-MM-DD HH:MM:SS. SELECT * means querying information on all columns.

We can also query only the information of some columns. For example:

• SELECT column1, column2 FROM table_name WHERE datetime_column >= start_time AND datetime_column <= end_time;

This statement means that only the two columns column1 and column2 are queried information.

2. Use php to connect to the database

Next, we need to use php to connect to the database. PHP provides many extension libraries to support different types of databases, such as mysqli, PDO, etc.

Here is mysqli as an example to demonstrate how to connect to the database:

In this example, we use the mysqli_connect() function to create a database connection. Among them, $servername, $username, $password and $dbname represent the database server name, user name, password and database name respectively. If the connection fails, the code will output "Connection failed". 
3. Use PHP to query the database
With the database connection, we can use PHP to query the database in the next step. First, we need to construct a sql query statement, and then use the mysqli_query() function to execute the query. 
In this example, we query the registration time of a user: 
= '$start_time' AND registration_time <= '$end_time'";

$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
    // 输出每行数据
    while($row = mysqli_fetch_assoc($result)) {
        echo "registration_time: " . $row["registration_time"]. "
";
    }
} else {
    echo "0 结果";
}

mysqli_close($conn);
?>
In this example, we constructed a SQL statement to query the registration time of a user in January 2021. Among them, $user_id, $start_time and $end_time are variables used to dynamically construct sql statements. Note that in the sql statement, we use single quotes to enclose $start_time and $end_time. This is because the time format is a string format and needs to be enclosed in single quotes. If you want to query a variable of numeric type, you don't need single quotes. Finally, use the mysqli_fetch_assoc() function to read the query results row by row. 
4. Use PDO to query the database
In addition to mysqli, there is also a common PHP database extension library-PDO (PHP Data Objects). PDO is a database abstraction layer across database platforms. It supports many different types of databases and has good performance. Using PDO is roughly like this: 
setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $start_time = "2021-01-01 00:00:00";
    $end_time = "2021-01-31 23:59:59";
    $user_id = 1;

    $sql = "SELECT registration_time FROM users WHERE user_id = :user_id AND registration_time >= :start_time AND registration_time <= :end_time";
    $stmt = $conn->prepare($sql);
    $stmt->bindParam(':user_id', $user_id, PDO::PARAM_INT);
    $stmt->bindParam(':start_time', $start_time, PDO::PARAM_STR);
    $stmt->bindParam(':end_time', $end_time, PDO::PARAM_STR);
    $stmt->execute();

    // 设置查询结果的返回模式为关联数组
    $stmt->setFetchMode(PDO::FETCH_ASSOC);
    // 输出每行数据
    while ($row = $stmt->fetch()) {
        echo "registration_time: " . $row["registration_time"]. "
";
    }
} catch(PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}
$conn = null;
?>
In this example, we use PDO to connect to the database and execute a SQL statement to query the user registration time. Compared with mysqli, PDO is more object-oriented in operation, easier to read and write. 
In short, whether using mysqli or PDO, PHP provides many convenient methods to query database information over a period of time. Developers can choose to use different methods according to their actual conditions. 
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