I am making a database, and to identify a client, their Tax Identification Number will be the Primary Key. ** Should the Tax Identification Number be VARCHAR, even though it's just numbers?**

I know things like phone numbers are more like addresses than numbers, and therefore should be VARCHAR.

I am not sure if the Tax Identification Number should be treated the same way, and I need to know these things before I work on the database since I am required to make a Entity Relationship Diagram of the database.

CodePudding user response：

If your are sure it's purely made up of numbers , why not use INT, which takes less disk space and less resource to index ? It's not like phone numbers , which sometimes may contain punctuation marks like hyphen. e.g 0064-337881

By the way, if data masking is required. An implicit convert is automatically performed so the INT type is cast into string type. e.g.
select insert(tax_id, 2 , 3, '***') from testtable;

result:

1***56

7***12

9***07