How to support custom fields for an entity and list them as columns? I am currently working on a system which supports "custom fields" for users. 

I will illustrate this with a simplified example of this database schema:

users
--------
user_id
name
age

custom_fields
----------------
custom_field_id 
custom_field_name

user_has_custom_field_value
------------------------
user_id (FK to users table)
custom_field_id (FK to custom_fields table)
custom_field_value (column that contains value of custom field)


This schema supports creation of custom fields to store information as per what the customer wishes. 

However, I want to list all users along with their custom fields in the query output (or by using some PHP logic)

|  user_id    |    name     |    age    |    fav_sport    |    payment_mode   |    bank 
----------------------------------------------------------------------------------
     3              John         28          Football           SWIFT             Chase
     6              Jane         24          Swimming           Cash               BOA      


fav_sport, payment_mode and bank are custom fields created which are represented as 3 rows in the custom_fields table.

So, the custom_fields table looks like this :

custom_field_id     |      custom_field_name 
-----------------------------------------------
       1                     fav_sport
       2                     payment_mode
       3                     bank


and the user_has_custom_field value looks like this :

user_id    |        custom_field_id     |       custom_field_value     
----------------------------------------------------------------------
   1                       1                          Football
   1                       2                           SWIFT
   1                       3                           Chase
   2                       1                          Swimming
   2                       2                           Cash
   2                       3                           BOA


What is the best way to achieve this with minimum queries and without taxing the database ?

The only solution I can come up with is by using a query inside a for loop in PHP to fetch the custom fields (which will definitely be heavy). What are more efficient solutions to do this ?

Suggestions welcome for MySQL based, PHP based, Stored Procedures etc.
You have two options: either you loop results from PHP, or you store all the custom fields and values in one single JSON datatype field (stored as a json object, requires MySQL 5.7) in the users table.