Good. Now, let's go deeper into table structure. Each column stores a certain type of data. Some columns store numbers (price, quantity, id), other columns store text (names, descriptions) or dates.
Why do we need to specify data types for columns? Couldn't there be one general data type for everything? Well, internally, our database performs a lot of bookkeeping. It needs to know how much space it should have for the data in a given column. A longer text requires more space than a short number, for example.
What's more, the database has many additional structures which make it run faster, like row sorting. Numbers are sorted differently than text. This is why we need to specify column types each time we add a column to a table.