I created a function to connect to the db in php:
function fn_connect($is_write = false)
{
$host = '127.0.0.1';
$db = 'name_db';
if ($is_write) {
$user = 'user_write';
$pwd = 'password_write';
} else {
$user = 'user_read';
$pwd = 'password_read';
}
$conn = new mysqli($host, $user, $pwd, $db);
if ($conn->connect_error) {
die('The database is not available. Please, try again later.');
}
return $conn;
}
When I need to connect, im calling it (and closing it) like this
$conn = fn_connect(true);
$stmt = $conn->prepare($q);
$stmt->execute();
....
$stmt->close();
$conn->close();
I thought it will be a good idea to verify if the connection exists, that way, I guess, I save connecting to the db every time for nothing, like this:
if (!isset($conn)) $conn = fn_connect(true);
$stmt = $conn->prepare($q);
$stmt->execute();
....
$stmt->close();
if (isset($conn)) $conn->close();
Is this a good idea, a good practice? Should I jut connect normally and let Apache/PHP do the rest (no need to verify nothing)?
It is good practiose and good style to check the connection, before letting php try to get or send data.
What is not good style is to use die in your connection, because it leaves a broken page.
Better is to design the page so that page still works when the connection is broken.
I try to make a simple IOS app that can connect to mysql database and read one table. But my php code does't work and really have no idea why, it's seems correct to me. The database is in a raspberry phpmyadmin server and the server works great.
I will put my code here and please tell me what's wrong.
<?php
$host = "192.168.2.193";
$db = "produtos";
$user = "root";
$pass = "1234";
$connection = mysql_connect($host, $user, $pass);
if(!$connection)
{
die("Database server connection failed.");
}
else
{
//attempt to select the database
$dbconnect = mysql_select_db($db, $connection);
//check to see if we could select the database
if(!dbconnect)
{
die("Unable to connect to the specified database!");
}
else
{
$query = "SELECT * FROM produtos";
$resultset = mysql_query($query, $connection);
$records = array();
//loop throught all our records and add them to our array
while ($r = mysql_fetch_assoc($resultset))
{
$records[] = $r;
}
echo json_ecode($records);
echo $resultset;
}
}
?>
Based on the question:
use mysqli_connect rather than mysql_connect because mysql_connect is deprecated and will not work someday. Also what is the the error you are getting? change your die() statement to something more helpful die(mysqli_error($connection));
Based on your comment:
That error would suggest that you either A) don't have the right IP address or B) there is a network issue between your host server and the SQL server, is this code running on the same server that is hosting the SQL database? if so then you can probably just use localhost for your $host
I am Developing the simple application,the application related to database operations.
My doubt is how can i connect to multiple databases same time.
how can php knows which databases the data will store.
If the user enter the data which database it will enter,both databases or one database.
Please answer my question.i have struggling a lot for this question.
If you use PHP5 (And you should, given that PHP4 has been deprecated), you should use PDO, since this is slowly becoming the new standard. One (very) important benefit of PDO, is that it supports bound parameters, which makes for much more secure code.
You would connect through PDO, like this:
try {
$db = new PDO('mysql:dbname=databasename;host=127.0.0.1', 'username', 'password');
} catch (PDOException $ex) {
echo 'Connection failed: ' . $ex->getMessage();
}
(Of course replace databasename, username and password above)
You can then query the database like this:
$result = $db->query("select * from tablename");
foreach ($result as $row) {
echo $row['foo'] . "\n";
}
Or, if you have variables:
$stmt = $db->prepare("select * from tablename where id = :id");
$stmt->execute(array(':id' => 42));
$row = $stmt->fetch();
If you need multiple connections open at once, you can simply create multiple instances of PDO:
try {
$db1 = new PDO('mysql:dbname=databas1;host=127.0.0.1', 'username', 'password');
$db2 = new PDO('mysql:dbname=databas2;host=127.0.0.1', 'username', 'password');
} catch (PDOException $ex) {
echo 'Connection failed: ' . $ex->getMessage();
}
Yes you can.. by using two connection strings..
$mysqli1 = new mysqli('HOST1', 'USER1', 'PASSWORD1', 'DB_NAME1');
$mysqli2 = new mysqli('HOST2', 'USER2', 'PASSWORD2', 'DB_NAME2');
and your queries should be like
$result1 = $mysqli1->query('query ......');
and
$result2 = $mysqli2->query('query ......');
Of course you can given example below add more connections if you want:
Class database
{
private oracleDatabase;
private mysqlDatabase;
public function connOracle() {
$db = "";
$user = "";
$password = "";
try {
$this->oracleDatabase = new PDO("oci:dbname=".$db,$user,$password);
} catch(PDOException $e){
echo "Can't connect to database (Oracle). ". $e->getMessage();
}
}
public function connMysql() {
$db = "";
$user = "";
$password = "";
try {
$this->mysqlDatabase = new PDO("mysql:dbname=".$db,$user,$password);
} catch(PDOException $e){
echo "Can't connect to database (Mysql). ". $e->getMessage();
}
}
}
Be carefull if you are using two databases on the same server at the same time. By default mysql_connect returns the same connection ID for multiple calls with the same server parameters, which means if you do
<?php
$db1 = mysql_connect(...stuff...);
$db2 = mysql_connect(...stuff...);
mysql_select_db('db1', $db1);
mysql_select_db('db2', $db2);
?>
then $db1 will actually have selected the database 'db2', because the second call to mysql_connect just returned the already opened connection ID !
You have two options here, eiher you have to call mysql_select_db before each query you do, or if you're using php4.2+ there is a parameter to mysql_connect to force the creation of a new link.
Use this below link to refer.What you have asked here.
PHP Documentation
Yes, you may use multiple database in one application, but the main thing is when you are communicating with the dbname, you have to specify that dbname also so than script will communicate with only that db in which you had defined. Ex.
$db1 = mysql_connect(...stuff...);
$db2 = mysql_connect(...stuff...);
mysql_select_db('db1', $db1);
mysql_select_db('db2', $db2);
$resultsa = mysql_query('SELECT * FROM table_a', $dbname) or die('Could not query database_a');
Yes you can connect multiple databases.
open your php.ini file and give me your database details like
port number,username,password.
And after that you can give the queries like this in your applications
$db1 = mysql_connect($hostname, $username, $password);
$db2 = mysql_connect($hostname, $username, $password, true);
mysql_select_db('database1', $db1);
mysql_select_db('database2', $db2);
Then to query database 1, do this:
mysql_query('select * from tablename', $dbh1);
and for database 2:
mysql_query('select * from tablename', $dbh2);
i think this is work fine for your question.
Yes you can, in very basic terms, you do it like this:
http://au1.php.net/function.mysql-connect
$conn = mysql_open($host, $username, $password, true);
To connect to multiple databases on the same server:
$dblink1 = mysql_select_db('database_a', $conn);
$dblink2 = mysql_select_db('database_b', $conn);
To get results from two databases:
$resultsa = mysql_query('SELECT * FROM table_a', $dblink1) or die('Could not query database_a');
$resultsb = mysql_query('SELECT * FROM table_b', $dblink2) or die('Could not query database_b');
edit - keep in mind that the mysql_ functions aren't available in recent PHP releases because they've been removed.
Warning
This extension is deprecated as of PHP 5.5.0, and will be removed in
the future. Instead, the MySQLi or PDO_MySQL extension should be used.
See also MySQL: choosing an API guide and related FAQ for more
information.
In my script I link to a page that connects to my database :
include "connect.php";
connect.php
<?php
error_reporting(E_ERROR);
/* Allows PHP to connect to your database */
// Database Variables
$Host = "myhost";
$User = "username";
$Password = "password";
$DBName = "database";
// Connect to Database
$connect = mysql_connect($Host, $User, $Password)
or die ("Could not connect to server ... \n" . mysql_error ());
mysql_select_db($DBName)
or die ("Could not connect to database ... \n" . mysql_error ());
?
Then in another script I have an insert query:
include "connect.php";
$Link = mysql_connect($Host, $User, $Password);
$Query = "INSERT INTO mytable VALUES ('0','".mysql_escape_string($forename)."','".mysql_escape_string($surname)."', '".mysql_escape_string($username)."', '".mysql_escape_string($password)."', '".mysql_escape_string($email)."')";
if(mysql_db_query ($DBName, $Query, $Link)) {
$message = "You have successfully registered";
header("Location: register.php?message=".urlencode($message));
} else {
die("Query was: $Query. Error: ".mysql_error($Link));
}
}
}
Why is this necessary :
$Link = mysql_connect($Host, $User, $Password);
Hasn't the connection already been established?
There is no point in doing this, especially as mysql_* functions will assume the last opened connection if none is given.
However, even with two calls to mysql_connect, only one connection is made. From the docs:
If a second call is made to mysql_connect() with the same arguments, no new link will be established, but instead, the link identifier of the already opened link will be returned. The new_link parameter modifies this behavior and makes mysql_connect() always open a new link, even if mysql_connect() was called before with the same parameters.
So by default, the existing connection will be returned.
I have an application where each user gets their own database where each database has the same schema.
I have a script that performs migrations in this fashion:
SHOW databases
Iterate through databases
Execute sql statements
This can take a long time when there are complicated queries that take a lot of time (3 or more seconds)
Is there a way where I can run the sql statements for each database at the same time from one script? Is this dangerous/too resource intensive to do this?
The reason I want to do this, is to prevent downtime as much as possible.
Here is my script now:
<?php
ini_set('display_errors', 1);
set_time_limit(0);
$sql = file_get_contents('../update.sql');
$sql_queries = explode(";", $sql);
$exclude_dbs = array('horde','phppoint_forums','phppoint_site','roundcube', 'pos', 'bntennis_site', 'mysql', 'information_schema', 'performance_schema');
$conn = mysqli_connect("localhost", "root", "PASSWORD");
$show_db_query = mysqli_query($conn, 'SHOW databases');
$databases = array();
while ($row = mysqli_fetch_assoc($show_db_query))
{
if (!in_array($row['Database'], $exclude_dbs))
{
$databases[] = $row['Database'];
}
}
foreach($databases as $database)
{
mysqli_select_db($conn, $database);
echo "Running queries on $database\n***********************************\n";
foreach($sql_queries as $query)
{
if (!empty($query))
{
echo "$query;";
if (!mysqli_query($conn, $query))
{
echo "\n\nERROR: ".mysqli_error($conn)."\n\n";
}
}
}
echo "\n\n";
}
?>
I don't know if the database will hold for that load but basically I would fork the process or spawn it into the background, depending on language.
For php you can fork the process for each database basically running the migrations in parallel.