How can I populate a custom field from the DB?

I need to populate a custom field in the item table from a MySQL query.

What's the best way to do this?

Thanks in advance for your help.

Hi,

At which time do you want to populate the custom field ?
And what kind of custom field ?

The solution, will be to edit the view displaying the custom field, make a request and fill the field value in php directly.
But I don't really understand your needs actually, because you can potentially the default value option to fill the custom fields by default.