How to filter customer by custom attribute using SQL query?

Question

The zd_user_id is our customer custom attribute.

$customerCollection = $this->customerFactory->create();
$customers = $customerCollection->addAttributeToFilter(
 [
 ['attribute' => 'zd_user_id', 'null' => true],
 ['attribute' => 'zd_user_id', 'eq' => ''],
 ['attribute' => 'zd_user_id', 'eq' => 'NO FIELD']
 ],
 '',
 'left'
)

How could I get all customers with the attribute zd_user_id equal true via SQL?

Answer 1

select * from eav_attribute where attribute_code='zd_user_id';

from this query, you get the attribute id and you also get the backend_type for this attribute.

Assuming the backend type is int.

select count(*) from customer_entity_int where attribute_id=<attribute_id_found> and value=1;

If it's varchar you can change the query to search in the table customer_entity_varchar.