Some definitions of foreign key:- A FOREIGN KEY in one table points to a PRIMARY KEY in another table. A foreign key is a field in a relational table that matches the primary key of another table. The foreign key can be used to cross-reference tables. A table may have multiple foreign keys, and each [...]

In my previous article (Magento: Very Useful Collection Functions), I had written about database interaction functions present in class Varien_Data_Collection_Db. Here, I am going to explain some database interaction functions present in the class Mage_Eav_Model_Entity_Collection_Abstract. These collection functions are very useful to select data from Magento database. We need them almost all the time for [...]

I got this error message when migrating my Magento files and database from one server to another. Notice: Undefined index: 0 in app/code/core/Mage/Core/Model/Mysql4/Config.php on line 92 Solution:

The JOIN keyword is used in an SQL statement to query data from two or more tables, based on a relationship between certain columns in these tables. [@via w3schools] A SQL JOIN clause combines records from two or more tables in a database. It creates a set that can be saved as a table or [...]

Suppose, you have a module called MyModule. Its version is 0.1.0. Now, you want to do some database changes for the module. You have the mysql setup file (mysql install file) mysql4-install-0.1.0.php in MyModule/sql/mymodule_setup folder of your module. You don’t need to make direct changes to database. You can upgrade your module to make your [...]

Difference between EAV and Flat Catalog In EAV database model, data are stored in different smaller tables rather than storing in a single table. Like, product name is stored in catalog_product_entity_varchar table product id is stored in catalog_product_entity_int table product price is stored in catalog_product_entity_decimal table

For using database, you need to install a package of PEAR called ‘MDB2’ along with the installation of PEAR and Smarty. MDB2 provides a common API for all support RDBMS.

1) To make a backup of a single MySQL database You have to make backup before you enter inside your MySQL system i.e. by typing mysql –u username –p password . (Here, username and password indicates your MySQL server username and password.)

Problem: “Fails to start the service. Please wait 30 seconds to try again.” I faced this problem 2 years back when I was a newbie to MySQL. I was just starting to learn PHP and MySQL at that time.