SQL server Table Structure Modification Method

What should we do if we need to modify the SQL server table structure? The following describes how to modify the SQL server table structure.

Add a varchar column to the SQL server table:
Alter table distributors add column address varchar (30 );
Delete a field from the SQL server table:
Alter table distributors drop column address RESTRICT;
Modify the types of two existing fields in one operation:
Alter table distributors
Alter column address TYPE varchar (80 ),
Alter column name TYPE varchar (100 );
Use a USING clause to convert an integer field containing UNIX timestamps to timestamp with time zone:
Alter table foo
Alter column foo_timestamp TYPE timestamp with time zone
USING
Timestamp with time zone 'epoch' + foo_timestamp * interval '1 second ';

Rename existing fields:
Alter table distributors rename column address TO city;
Change the name of an existing SQL server table:
Alter table distributors rename to suppliers;
Add a non-empty constraint to a field:
Alter table distributors alter column street set not null;
Delete A non-empty constraint from a field:
Alter table distributors alter column street drop not null;
Add a check constraint to a table:
Alter table distributors add constraint zipchk CHECK (char_length (zipcode) = 5 );
To delete a table and all its sub-tables, follow these constraints:
Alter table distributors drop constraint zipchk;

Add a foreign key constraint to the table:
Alter table distributors add constraint distfk foreign key (address) REFERENCES addresses (address) match full;
Add a unique (Multi-field) constraint to the table:
Alter table distributors add constraint dist_id_zipcode_key UNIQUE (dist_id, zipcode );
Add an automatically named primary key constraint to a table. Note that a table can only have one primary key:
Alter table distributors add primary key (dist_id );
Move the table to another tablespace:
Alter table distributors set tablespace fasttablespace;