Question

I Know there can’t be more than 1 primary key in a table but what is the technical reason ?

Answer 1

Pulled directly from SO:

You can only have one primary key, but you can have multiple columns in your primary key.

You can also have Unique Indexes on your table, which will work a bit like a primary key in that they will enforce unique values, and will speed up querying of those values.

Primary in the context of Primary Key means that it’s ranked first in importance. Therefore, there can only be one key. It’s by definition.

It’s also usually the key for which the index has the actual data attached to it, that is, the data is stored with the primary key index. Other indices contain only the data that’s being indexed, and perhaps some Included Columns.