What is a primary key? Is it a type of index? How do I create one in SQL Server?
A PrimaryKey of a table uniquely identifies each record.
In SQLServer, when you create a Primary Key, it's implemented as a unique clustered index on the column or columns (if there's not already a clustered index on the table and you don't specify a unique nonclustered index).
Once inplace, it means that inserts or updates that would create non-unique records are rejected. In SQLServer, primary key column's cannot allow NULL values.
In the table designer, you can create one by highlighting the column or columns and clicking on the key symbol in the toolbar.
Or you can use TSQL's CREATE TABLE statement which is described here
Strictly speaking a Primary Key is a CONSTRAINT, not an index.
However when you specify one, SQL Server implements the uniqueness by creating a UNIQUE INDEX for the columns that you have specified for the primary key. This differs from a unique constraint in the fact that the columns in a PK are not allowed to be nullable [whereas a unique constraint will allow one and only one null]
As already noted, by default SQL will attempt to make the PK a clustered index, but you can specify it to be non-clustered.
Having a PK allows a FOREIGN KEY to reference the table (although UNIQUE INDEX or UNIQUE CONSTRAINT also allow this)
You can only have one PK per table.
Primary Key is a unique value that is used to identify a row in a table. The primary key can be anything in the table which is unique for a row. Here we can take the phone no also a Primary key because it is unique for every person.
read more about primary key and difference between foreign key and primary key on https://www.scaler.com/topics/difference-between-primary-key-and-foreign-key/#what-is-primary-key-
1 Person is following this question.