[sql-server] How can I alter a primary key constraint using SQL syntax?

I have a table that is missing a column in its primary key constraint. Instead of editing it through SQL Server, I want to put this in a script to add it as part of our update scripts.

What syntax can I use to do this? Must I drop and recreate the key constraint?

you can rename constraint objects using sp_rename (as described in this answer)

for example:

EXEC sp_rename N'schema.MyIOldConstraint', N'MyNewConstraint'

In my case, I want to add a column to a Primary key (column4). I used this script to add column4

ALTER TABLE TableA
DROP CONSTRAINT [PK_TableA]

ALTER TABLE TableA
ADD CONSTRAINT [PK_TableA] PRIMARY KEY (
    [column1] ASC,
    [column2] ASC, 
    [column3] ASC,
    [column4] ASC
)

Performance wise there is no point to keep non clustered indexes during this as they will get re-updated on drop and create. If it is a big data set you should consider renaming the table (if possible , any security settings on it?), re-creating an empty table with the correct keys migrate all data there. You have to make sure you have enough space for this.

PRIMARY KEY CONSTRAINT cannot be altered, you may only drop it and create again. For big datasets it can cause a long run time and thus - table inavailability.