Magento – Changing attribute dropdown to radio buttons

Let's take them one by one.

1. You should use the int values for consistency. But (as you saw) it works with varchar also. I have a hunch it works with text too.

2. "how did this dropdown attribute get created as an int backend but ended up in the catalog_product_entity_varchar". That's a complete mystery. Only the original developer can tell you that (maybe not even him). But I can tell you how is possible to reference the eav_attribute_option table. It's because the attribute options do not care about the type of the attribute. If the attribute has a source_model it calls getAllOptions from that source model and matches the value set on the product with what it finds in the result of getAllOptions.

3. I think the answer to number 2 will answer number 3 also. In addition is because PHP is a loose type programming language and 3 == "3" evaluates to true.

To change the attribute type you can create a set-up script and call the following snippet:

$installer->updateAttribute('catalog_product', 'your_attribute_code', array(
    'type' => 'varchar',
    'input' => 'text',
));

But this will not copy over the currently set values on the products. I am not sure what the best way to cover this would be. Though I can give you the following information:

1. catalog_product_entity_int: will store the id of the options selected,
2. catalog_product_entity_varchar: is where the varchar attribute values should be stored,
3. eav_attribute_option: this will give you the link from options to attributes,
4. eav_attribute_option_value: this will give you the text value for each of the attribute's options,

From this you should be able to copy all the attribute values from the integer values stored in catalog_product_entity_int and make them the relevant text values stored in catalog_product_entity_varchar