php+mysql database query example, mysql example_PHP tutorial

//Parameters for connecting to the database
$host = "localhost";
$user = "root";
$pass = "zq19890319";
$db = "phpdev";
//Create a mysql connection
$connection = mysql_connect($host, $user, $pass) or die("Unable to connect!");
//Select a database
Mysql_select_db($db) or die("Unable to select database!");
//Start query
$query = "SELECT * FROM symbols";
//Execute SQL statement
$result = mysql_query($query) or die("Error in query: $query. ".mysql_error());
//Display the number of rows in the returned record set
If(mysql_num_rows($result)>0){
//If the number of rows in the returned data set is greater than 0, it will start to be displayed in table form
echo "";
​​​​while($row=mysql_fetch_row($result)){
echo "";
echo "";
echo "";
echo "";
echo "";
                                                                                                              echo "

".$row[0]."

".$row[1]."

".$row[2]."

";
}  
else{
echo "Record not found!";
}  
//Release the memory occupied by the record set
Mysql_free_result($result);
//Close the database connection
Mysql_close($connection);
?>

The above code analysis is as follows:

1. Establish a connection to the database server. This information includes the server address, MySQL username, password, and selected database name. These variables are stored in PHP variables.

2. Once communication is established with the MySQL database server, the database server needs to open a connection. All communication between PHP and the database passes through this connection. In order to initialize this connection, PHP provides the mysql_connect() function. This function includes three parameters, all of which are required, namely database server name, username and password. If both the database server and the web server are running on the same machine, you can use localhost as the server name. mysql_connect() returns a "connection identifier", which is stored in the variable $connection. This identifier is used to communicate with the database.

3. After using $connection to connect to the database, you need to use the mysql_select_db() function to select a database.

4. Create a query and execute it. We use the mysql_query() function to implement this function.

5. If mysql_query($query) is executed successfully, the returned result record set will be stored in the $result variable. This result set may contain one or more rows or columns of data, depending on the query command used. Depending on the returned results, we can use the mysql_fetch_row() function to process the result data into a single-column array, which is stored in the $row array. Field values ​​in this array can be accessed continuously using standard PHP array notation. Each time the mysql_fetch_row() function is called, the next record in the result set will be returned. This feature makes mysql_fetch_row() very suitable for while and for loops.

6. Since the result set returned after each query occupies memory, we use the mysql_free_result() function to release memory. After the result set is released, if there are no other query operations, you can use the mysql_close() function to close the connection with the MySQL server.

I hope this article will be helpful to everyone’s PHP programming design.