Find duplicated taxvat (DNI, NIF) in database for Magento 1

Just a quick note for myself. If we need to find duplicated values for a specific attribute (in this case attribute “taxvat” for the entity “customer” (for Magento 1):

• First of all, we need to know the attribute id of our attribute code:

select attribute_id,attribute_code from eav_attribute where attribute_code = 'taxvat';

• And then we execute the following query to find all the entries that are duplicated:

select value, count(*) c from customer_entity_varchar where attribute_id = '15' group by value having c > 1;