how to assign default value in sql code example

Example 1: default number in sql

//Sql Server

//Add a table 
ALTER TABLE clients ADD Points INT DEFAULT 0
//Edit an existing table
ALTER TABLE clients ADD CONSTRAINT points DEFAULT 0 FOR Points

Example 2: sql default

Sets a default value for a column;
Example 1 (MySQL): Creates a new table called Products which has a
name column with a default value of ‘Placeholder Name’ and an available_
from column with a default value of today’s date.
CREATE TABLE products (
id int,
name varchar(255) DEFAULT 'Placeholder Name',
available_from date DEFAULT GETDATE()
);
Example 2 (MySQL): The same as above, but editing an existing table.
ALTER TABLE products
ALTER name SET DEFAULT 'Placeholder Name',
ALTER available_from SET DEFAULT GETDATE();