How to use php to query the database to satisfy three fields at the same time

PHP is a scripting language widely used in Web development, and querying the database is a common operation in Web development. Especially when collecting and displaying data, you need to query data from the database. In database query operations, queries that satisfy multiple conditions are very common. This article will introduce how to use PHP to query the database to satisfy three fields at the same time.

In PHP, we can use database extensions such as mysqli or PDO to connect to the MySQL database and perform database query operations. The following uses the mysqli extension as an example to introduce how to query three fields at the same time.

Step 1: Connect to the database

When using the mysqli extension for database operations, we need to first connect to the mysql database through the mysqli_connect() function. This function has four parameters, namely the server address, Username, password and database name.

The sample code is as follows:

$servername = "localhost";
$username = "root";
$password = "";
$dbname = "test_db ";

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

if (!$conn) {

die("连接失败: " . mysqli_connect_error());

}

echo "Connection successful";

Step 2: Write SQL query statement

We can use SELECT and WHERE clauses to write SQL query statements, and the SELECT clause is used to select the query Data table fields, WHERE clause is used to specify query conditions. When the query satisfies three fields at the same time, we can use the AND operator to connect multiple query conditions.

For example, if we want to query the records of name='Zhang San', age=18, gender='male' in the students table, we can use the following SQL query statement:

$sql = " SELECT * FROM students WHERE name='Zhang San' AND age=18 AND gender='male'";

Step 3: Execute SQL query statement

You need to use mysqli_query( ) function, this function has two parameters, one is the variable name to connect to the database, and the other is the SQL query statement. After successful execution, the mysqli_query function will return a result set object.

The sample code is as follows:

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

if (mysqli_num_rows($result) > 0) {

while($row = mysqli_fetch_assoc($result)) {
    echo "姓名: " . $row["name"]. " - 年龄: " . $row["age"]. " - 性别: " . $row["gender"]. "<br>";
}

} else {

echo "0 结果";

}

Step 4: Complete sample code

The following is a complete sample code for querying three fields at the same time Record:

$servername = "localhost";
$username = "root";
$password = "";
$dbname = "test_db" ;

//Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
//Detect connection
if (!$conn) {

die("连接失败: " . mysqli_connect_error());

}

echo "Connection successful";

//SQL query statement
$sql = "SELECT * FROM students WHERE name='Zhang San' AND age =18 AND gender='male'";

//Execute query operation
$result = mysqli_query($conn, $sql);

//Output query results
if (mysqli_num_rows($result) > 0) {

while($row = mysqli_fetch_assoc($result)) {
    echo "姓名: " . $row["name"]. " - 年龄: " . $row["age"]. " - 性别: " . $row["gender"]. "<br>";
}

} else {

echo "0 结果";

}

// Close the connection
mysqli_close($conn);
?>

Summary

PHP is a powerful web development language and has many flexible methods in database operations. This article introduces how to use the mysqli extension to connect to the MySQL database and query three fields at the same time in PHP. Understanding this basic query method can help us better apply PHP for database development and quickly realize business function requirements.

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