I am using one db file to connect to the database. However, i need to show something else from another db database on this site. I can't use two db connect files. So, how do i go about display one websites content on another website with two different connections.
For one thing, you don't need separate database connections to the same server. Simply specify the database name before each table name in your SQL statements. For example:
SELECT foo, bar FROM db.table;
rather than:
SELECT foo, bar FROM table;
For another, you shouldn't be storing the database connection in a global for just the sort of reason you're running into. I suspect you're using the outdated mysql extension, which uses an implicit DB connection resource whenever one isn't explicit. Switch to PDO and create a simple connection manager class. One big advantage to PDO is it supports prepared statements, which can be safer and more performant than what the mysql extension provides. If you need a PDO tutorial, try "Writing MySQL Scripts with PHP and PDO"
If it is a separate db server you might need to look into the mysql federated engine which allows you to link to databases on separate servers as if they were on the same host.
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In MySQL, I have two different databases -- let's call them A and B.
Database A resides on server server1, while database B resides on server server2.
Both servers {A, B} are physically close to each other, but are on different machines and have different connection parameters (different username, different password etc).
In such a case, is it possible to perform a connection between a table that is in database A, to a table that is in database B of different servers?
If so, how do I go about it, programatically, in php? (I am using php, MySQLDB to separately interact with each one of the databases).
The only way I can think of, is by opening 2 separate connections (i.e. instantiate 2 PDO objects) with all the different parameters, use 2 queries to query all the data you need into PHP, and then work with that on PHP.
You can make two separate MySQL connections in PHP, do two queries to the two tables, and then work with the results in PHP.
Another option, since the servers are physically close, is to setup the one or both servers to replicate the needed database/tables to each other. You can look here for more on MySQL replication:
http://dev.mysql.com/doc/refman/5.6/en/replication.html
How can i access in two different databases at the same time, i mean can i implement a search from database1 and save for example the id or another information to a database2?
If you have a user account that can access both databases, just prefix the database name:
SELECT database1.table1, database2.table2.....
as far as I know, you can even do JOINs, although I don't know about possible performance implications.
If you do not have a mySQL account that can access both databases, it's not possible.
Yes. PHP has a few MySQL extensions. However, if you're just getting started, look at the MySQL functions for this. Specifically mysql_connect() and mysql_select_db() could be used to create separate connections to different databases or switch between them on the same connection.
I have a working PHP server. Now I want to use databases (MySQL or something similar). Is it possible to create a database from PHP?
I would like to emphasize that in my case I do not have any user-name and password which I can use to connect to MySQL server. I also do not have a control-panel where I could create a database or a table in an existing database.
ADDED:
I think SQLite is what I need. But if I try to create a new database from PHP I see that PHP tries to create a file in a directory which is different from the directory where my files are supposed to be. Then it reports that it is unable to create the database and I think it is because it tries to create in the directory to which I have no permission to write. Can I force PHP to create SQLite in a specific directory?
I'm assuming you want to create an SQL database without access to a stand-alone database server. You could use SQLite, which is a library that creates a lightweight database in a single file without separate processes.
It's not quite as efficient as a standalone database server, however, so if you need performance, use a proper database server. It's not an unreasonable requirement for a high-performance web app.
Mysql,no. SqlLite is a possibility, you only need write permissions on the filesystem.
www.sqlite.org/
I would like to emphasize that in my
case I do not have any user-name and
password to which I can use to connect
to MySQL server. I also do not have a
control-panel where I could create a
database or a table in an existing
database.
This question is confusing to me, because if you're using MySQL you should be able to create a database, with a username and password to connect, using their command line admin tool. That's also the way to create a database or a table as well.
Are you saying you don't have access to the admin tool? You don't have an account? If so, you'll need to ask for them from the person who does have such access.
An option is to set up an SQLite database in a directory outside of your htdocs folder. This is so people can't type in the name of the database file and download the entire database, severely compromising security.
If you are so inclined, you can even set up a layer of abstraction between PHP and the DBMS using PDO. Then, in order to create the database object, you would specify a DSN specific to SQLite write something like this:
$pdo_obj = new PDO('sqlite:/path/to/my_database.sqlite3');
and then query it like a normal PDO object using the PDO functions.
This method would better allow for easier migration to using a client-server DBMS once you can get one set up; it would just be a matter of copying the table structure and data over to the new database, and changing the DSN to something appropriate.
Creating a database through PHP is possible, but for that you need a connection to the database, which needs a username/password pair or some kind of authentication. Unless your database allows anonym logins or something similar, it's not possible.
Yes, just fire a create database sql query from PHP
http://dev.mysql.com/doc/refman/5.0/en/create-database.html
I've heard that SQLite can do this (to avoid synchronicity issues in heavy traffic scenarios) is this true? If so how would I do this with PDO in PHP?
Would you be looking for the ATTACH and DETACH sqlite commands? You can call these with a query to any SQLite PDO object.
The commands allow you to attach a separate database file to the current session. An example would be:
$connection->query('ATTACH DATABASE blog_entries.sqlite AS BlogEntries;');
You can then refer to the tables located in the attached database by their name (eg: SELECT * FROM entries) if there is no duplicate tables. If there is a conflict then they need to be namespaced with the database alias (eg: SELECT * FROM BlogEntries.entries)
Reference: SQLite Manual
You can open a DB in memory (I believe the DSN for PDO is sqlite:memory:) and attach the different databases.
I'm wondering how slow it's going to be switching between 2 databases on every call of every page of a site. The site has many different databases for different clients, along with a "global" database that is used for some general settings. I'm wondering if there would be much time added for the execution of each script if it has to connect to the database, select a DB, do a query or 2, switch to another DB and then complete the page generation. I could also have the data repeated in each DB, I just need to mantain it (will only change when upgrading).
So, in the end, how fast is mysql_select_db()?
Edit: Yes, I could connect to each DB separately, but as this is often the slowest part of any PHP script, I'd like to avoid this, especially since it's on every page. (It's slow because PHP has to do some kind of address resolution (be it an IP or host name) and then MySQL has to check the login parameters both times.)
Assuming that both databases are on the same machine, you don't need to do the mysql_select_db. You can just specify the database in the queries. For example;
SELECT * FROM db1.table1;
You could also open two connections and use the DB object that is returned from the connect call and use those two objects to select the databases and pass into all of the calls. The database connection is an optional parameter on all of the mysql db calls, just check the docs.
You're asking two quite different questions.
Connecting to multiple database instances
Switching default database schemas.
MySQL is known to have quite fast connection setup time; making two mysql_connect() calls to different servers is barely more expensive than one.
The call mysql_select_db() is exactly the same as the USE statement and simply changes the default database schema for unqualified table references.
Be careful with your use of the term 'database' around MySQL: it has two different meanings.