I want to show you some of the features, really, of what Create Table can do. In this particular instance, if you notice Create Table, I'm creating a table called Products. Here, I'm specifying my columns; product_id, product_name, product_cat, and it's a primary key. Here's the thing though, primary key is not a column. This is what's called a constraint. Primary key is a constraint. Primary key has three characteristics; primary key cannot be null, it has to be unique, and primary keys are indexed. They are indexed so that they're very easily searchable and very quickly searchable. So not null, they're unique to the table, and they are indexed. Primary key is a constraint that is set. Also, if you notice right here, product_id is going to be a number, data type, so that's a data type right there. Here, I'm specifying what's going to go inside of that product_id. I'm saying the product_id will be a number that is going to be generated. Generated applies to the column, believe it or not. It's going to be generated, and it's going to be generated as an identity. Now, identity is also a internal within Oracle SQL. That identity column specification, this generated default. Generated default as identity essentially means that the product_id column will automatically create a number starting at one and then incrementing by one each time. It that generated by default as identity. If you happen to delete a row and add a new row, it will continue on from where the number left off. Let's say you added three rows, 1, 2, and 3, and then I created a product_id, of course, with 1, 2, and 3 and you happen to get rid of number 3, you happen to get rid of that row and you added a new row, it will not replace it with the 3. It will start with a 4. It's as if 3 never existed. It only counts up, basically makes certain that the product_id remains unique. That's why the product_id in this particular instance is generated as an identity column, starts with 1 and increments by 1 with each new addition of a row. This is a Create Table. Then I am altering the table, which means I'm going to manipulate a table that already exists. You cannot alter a table unless a table exists already. Here's a Create, and then here is an Alter, so modify the table. I'm going to add a couple of columns in this table. I'm going to add a column called created_at and another column called updated_at. Both of those columns will be of timestamp data type. Timestamp data type is a data type, just like varchar2 is a data type, just like number is a data type. Timestamp is a data type that accepts timestamp.
