In order to properly understand Oracle syntax, you need to work with it by hand. Let me show you what I mean. When you do a create table syntax, you need the words create and the word table followed by whichever table you are creating. So start, create command, the table command followed by the name of the table. That's not enough. You have to specify what you want in there. In SQL Plus which is the tool that I'm using, these two means, I want the second line of my create table statement. It doesn't know what I want to do. It just gives me the second line because I pressed Enter over here, and it knows that create table customer is not a complete statement. Statements are completed in SQL Plus by specifying the semicolon. Here I have to open parentheses. Opening parentheses after the create table customer allows me to specify the columns I want. If I say customerID, notice the way I have written customerID out. This is called camel casing. It's the lowercase start, and then an uppercase after each syllable or new word. Here I've got customerID and I'm going to specify that this is going to be a integer datatype. There are many numeric data types that exist in Oracle. Double is one of them, int is another one, number is another one, currency is another one. I just specified int for integer because I know that customerID is going to be a positive number and it's going to be a whole number, is going to specify the unique row value, then I put a comma. This is the opening parentheses followed by the name of the column, followed by the data type of the column, followed by a comma. Comma means I want to specify the next column. It all started with create and then a table, and the name of the table customer. Since I have not specified a semicolon, SQL Plus is not going to attempt to run this command just yet. When I press "Enter", it gives me a third line essentially telling me that, "Okay, you're not done yet because you haven't specified a semicolon." Then I'm going to say customerName and it's going to be a variable-length character. I should spell that properly, with a maximum of 20 character datatype. When I specify a comma here, it signals that I'm going to specify my next column. The name of this column is customerName. The data type of the column is variable-length character which means this particular column will have alphanumeric characters that will be up to 20 characters in length. The reason I specified variable length characters because I know for a fact that customer names will be no more than 20 characters in length or up to 20 characters in length, which means that I want the database to use exactly the number of characters that this particular column takes up. If customerName is Abc Corp, I just want to take up the amount of space required to store Abc Corp. If the customer name is longer, I wanted to use up the space needed for that longer customerName up to 20 characters. If the customerName is greater than 20 characters, I'm going to get an error letting me know that, "Hey, I'm trying to enter a customer name that's larger than 20 characters." It may even result in the truncating or chopping off the customerName at the 20 character mark. That's why it's very important to know how big each field is going to be, because integer is a numeric field, automatically assigns the value, the maximum value, positive or negative, and it is going to be a whole number. I will specify a decimal field like a decimal, like a double, like a float which would allow me to state the number of decimal places I want. CustomerID is going to be a whole number. These open and closed parentheses here, are supposed to be inside of the datatype, variable length character signaling how big this data is going to be, how many characters customerName is going to eat up. That has to be in open, close parentheses. This closing of parentheses right here, closes the actual columns that I've specified right there. This, I can complete by doing and specifying a semicolon. When I specify semicolon here, it signals to SQL Plus that this whole command has been completed. As you can see when I press "Enter", it created the customer table for me. That semicolon is what signaled that the table was ready to be created.
