Let's show some examples of the alter table command. If I do a create table products, and I say that I'm going to have a product_id, and I'm going to make it a number, and I'm going to say that it's going to be generated by default, and it's going to be a identity column which means that it's going to put in values itself, starting at 1 and every row is going to get a unique identity, never repeating. This is going to be product name, variable length character 2-20 characters, product category is going to be a variable and character 2-20 like so. Then I'm going to say that the primary key, which means it's going to be a unique identifier, primary key is a constraint, which means that I'm going to make sure that the product_id is not repeated, and that it is searchable. Search it, and there is the table products constructed right over here, and there is the products table. There's product_id, product_name, and product_cat, or for product category. I'm going to do something else. Right now I've got these three columns. I'm going to do this. I'm going to say I'm going to alter table products, and I'm going to add created_on. I'm going to make that a timestamp column. I'm going to include the time zone in that column. I'm going to make sure that is not null. Not null is a constraint. I'll open this thing up here. That's adding that, created_on. I'm going to do a updated_on, and I'm going to say that's going to be a timestamp, and I'm going to include time zone, make sure that's not null as well. Run that. Done. Now when I refresh products over here, notice, created_on, updated_on. It added these two columns, and their timestamp columns. Now what I'm going to do is I'm going to do a insert into products, and I'm going to include in here product_name, product_cat. I'm also going to include created_on and updated_on. The reason for that is because these two columns, created_on and updated_on cannot be blank. Notice they say, it cannot be null. Those are constraints; cannot be null, so to put values in there. I'm going to say product name, I'm going to say eggs, and then the product category, grocery. I'm going to say current timestamp once and current timestamp twice. What this is, this timestamp is going to go inside of updated_on, right here, and this timestamp right over here is going to go in created_on. I'm going to add this, run this, and it ran. Notice it says one row inserted. I'm going to put another one in there. I'm going to say bread, and run this. Then I'm going to say cheese. Also part of groceries. Run that. Then I'm going to take a look. I'm going to do select everything from the products table. Let's take a look. There's the product_ids: eggs, bread, and cheese, they're all groceries, and here are the timestamps on when these were inserted. That's an example of a alter table. I altered the table, added some columns with some constraints, auto-generated keys, making it a primary key. I wanted to show you all that.
