Best way store an array of items with details in SQL table

Question

I'm trying to find out the best way store array of items with details in SQL table. I have a user account database. The user have multiple input fields to enter multiple details like:

___ : ______ +(get more multiple field field)

User can input any details like

Output1 : Output2
Mobile : 2455...
email : sdf
city : dfs
Other : sf

On an average a user will use around 20 options

Since the fields (mobile, email etc.) are not known to me, I have to store Output1 field with the answer field ( output2 ).

I will be having a very huge user base, so I think it's not better to create separate tables for each user.

Is there any way to store and get the details in limited or single column.

Answer 1

Since both the attribute name and value comes from users, a typical 3-table model of saving many-to-many relationship is a bit of overkill.

I would just kept users and their attributes in two separate tables:

+---------+-----------+--------------+
| user_id | user_name | user_email   |
+---------+-----------+--------------+
| 1001    | John      | john@doe.com |
+---------+-----------+--------------+
| 1002    | Tim       | tim@doe.com  |
+---------+-----------+--------------+

+----------+-----------+--------------+--------------+
| field_id | user_id   | field_name   | field_value  |
+----------+-----------+--------------+--------------+  
| 1        | 1001      | Option1      | Option2      |
+----------+-----------+--------------+--------------+
| 2        | 1001      | Mobile       | 2345656565   |
+----------+-----------+--------------+--------------+
| 3        | 1001      | city         | dfs          |
+----------+-----------+--------------+--------------+
| 4        | 1002      | Other        | something    |
+----------+-----------+--------------+--------------+

Possibly with some additional columns for sorting, tagging, etc.

Answer 2

I would use 3 tables.

Table 1 - user. PK is UserId. Other fields are name, rank, serial number, etc

Table 2 - Attribute - Primary key is AttributeId. Other Field is attribute name. Examples of attribute names are emailAddress, cellphoneNumber, cityName.

Table3 - UserAttribute. Primary Key is UserId and AttributeId. Other field is Attribute value.