Query multiple databases in the same query

[cyberRobot]

When querying tables that are stored in different databases, I normally establish separate database connections, run separate queries, and combine the results in PHP. However, it appears that you can connect to one database and run a joined query on both databases, as long as the login credentials work for both databases.

 

With that said, does anyone know of an issue with writing a query like the one below?

SELECT 
    alias1.columnName1, 
    alias2.columnName2 
FROM       database1.table1  AS alias1 
LEFT JOIN  database2.table2  AS alias2  ON ...

 

Note that I wouldn't use names like database1, alias1, etc. And you can ignore the "..." in the ON clause. 

[Barand]

However, it appears that you can connect to one database and run a joined query on both databases, as long as the login credentials work for both databases.

Yes, that's OK. So long as they are both on the same server. The connection is to the server. And, as you said, you have privileges to access all databases in the query.

Edited December 7, 2016 by Barand

[cyberRobot]

Thanks Barand!