How to query data in php

PHP is a commonly used server-side scripting language widely used in the field of web development. In web development, querying the database is one of the essential operations. PHP supports multiple database types, such as MySQL, PostgreSQL, Oracle, etc. This article will take the MySQL database as an example to introduce how to use PHP for data query.

1. Connect to the database

In PHP, to query the database, you first need to establish a connection with the database. The method to connect to the MySQL database is as follows:

$conn = mysqli_connect($servername, $username, $password, $dbname);

Among them, $servername represents the name or IP address of the database server, $username represents the user name of the database account, $password represents the password of the database account, and $dbname represents the database to be connected. Name database. The above code will return a database connection object $conn. We can determine whether the connection is successful by calling the mysqli_connect_errno() and mysqli_connect_error() functions and output the error message:

if (mysqli_connect_errno()) {
    echo "连接 MySQL 数据库失败：" . mysqli_connect_error();
    exit;
}

2. Query data

After the connection is successful, we can use SQL statements to query the data in the database. The most basic query statement in MySQL is SELECT, and the syntax is as follows:

SELECT column_name(s) FROM table_name WHERE condition;

Among them, column_name(s) indicates the column name to be queried, and * can be used to indicate querying all columns; table_name indicates the table name to be queried; condition Indicates query conditions, and multiple conditions can be used, such as AND, OR, NOT, etc.

For example, query the names and phone numbers of all customers in the customer table:

$sql = "SELECT name, phone FROM customer";
$result = mysqli_query($conn, $sql);

mysqli_query() function is used to execute SQL statements and return a result set object $result. We can call The mysqli_num_rows() function obtains the number of rows in the query result and obtains each row of data by looping through the result set object:

if (mysqli_num_rows($result) > 0) {
    while ($row = mysqli_fetch_assoc($result)) {
        echo "姓名：" . $row["name"] . "，电话：" . $row["phone"] . "<br>";
    }
} else {
    echo "没有查询到数据！";
}

mysqli_fetch_assoc() function is used to obtain a row of data in the result set object and store the data in the association in array $row. We can get the value of the specified column through $row[column name].

3. Close the database connection

After the query is completed, in order to release resources and protect the security of the database, we need to close the connection with the database. The method to close the connection is as follows:

mysqli_close($conn);

Full code example:

Summary

The above is the basic PHP method to query the MySQL database. Of course, actual development also involves more complex query operations, such as connecting multiple table queries, grouping queries, subqueries, etc. Appropriate query statements and methods need to be selected according to the actual situation.

At the same time, when using PHP to query the database, to ensure data security, you should use prepared statements and bound parameters to avoid security issues such as SQL injection.

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