In SQL Server:

1. When a Primary Key is dropped, SQL Server:

   • Removes the NOT NULL constraint from the column if it was only enforced via the PK.

   • It does not automatically change any values to NULL.

2. So how did the NULLs get there?

   • Those rows were probably already there, but the column had default values (e.g., autogenerated or inserted earlier).

   • Once you dropped the PK and altered the column to allow NULLs (or SQL Server did that for you), subsequent operations (like inserts) may have inserted NULL into those rows — especially if:

     • There was no default value set.

     • Your application/data import inserted rows without setting a value for that column.

What to do now:

🔹 1. Check how many NULLs you have:

SELECT COUNT(*)

FROM YourTableName

WHERE YourColumnName IS NULL;

2. Inspect some of those rows

SELECT* FROM YourTableName

WHERE YourColumnName IS NULL;

3. Remove them

Delete FROM YourTableName

WHERE YourColumnName IS NULL;