How to modify the table structure in SQL Server

Once the table is created in SQL Server, you can modify the table structure either through GUI or through script. I am going to list down the possible cases of updating the table structure

Add a column:

ALTER TABLE "TABLE-NAME" ADD "COLUMN-NAME" varchar(50) NULL

Modify the Data Type:

ALTER TABLE "TABLE-NAME" ALTER COLUMN "COLUMN-NAME" "NEW DATA TYPE" NULL

Modify the NOT-NULL Constraint:

ALTER TABLE "TABLE-NAME" ALTER COLUMN "COLUMN-NAME" VARCHAR(30) NOT NULL