What is a primary key?
The primary key is the first thing you need to know about a product, because all the other keys are secondary.
A primary key is a feature that gives you a competitive advantage.
You might have heard of them, probably if you are an entrepreneur or a developer: “Doing without it”; “A blank canvas”; “The king of the hill”; etc.
All great words, but none of them actually describe what a primary key does. They are simply words for things that exist, but don’t actually deliver on the features they promise (for example: you can use a blank canvas to generate any image you want). Some companies know this, and that is why they use them to describe their products; others do not.
There are only two true answers here: 1) You should find out what they do and 2) You should build your own primary key. And since finding it is the easy part, we will focus on building one here. But before we go further, let’s briefly talk about “what is a primary key?”
The term was coined by Steve Blank in his seminal book The Startup Owner’s Manual (it was later expanded into The Startup Owner’s Guide). It refers to a feature or set of features which give you an advantage over your competition. Each product has its own set of features — some are more obvious than others — and each company has its own set of features that distinguish it from its competitors. For example, Gmail has search and IMAP email support (which makes it great for work-related communications) but does not have built in calendar capabilities (because it doesn’t compete with Google Calendar). So when people look at Gmail vs. GMail vs. Yahoo mail, they often make the mistake of assuming that Google Calendar wins every time (which isn’t how competition works). In short, Google Calendar does not win every time because there are many other competing products out there which offer similar functionality and perform better than Google Calendar in some cases! So your job as the startup owner is to come up with the best solution to your customers’ needs and make sure you nail it!
In addition to those three things above, we will also include: 1) A research roadmap 2) A product roadmap 3) Your product roadmap 4) Your value proposition 5) Your customer journey 6) What will be different/differentiate between yours and your competitors 7) Other things need time to figure out 8) How much time do we have 9
How to define a primary key in Oracle?
There are a number of ways to define a primary key. In Oracle, you can use the CREATE TABLE statement only, or you can add a column in the database called “primary_key” which is a hash of the primary key using either the MD5 or SHA-1 algorithm. For example:
CREATE TABLE table_name ( id INTEGER PRIMARY KEY , name CHAR(32), email VARCHAR(40) ); CREATE TABLE table_name ( id INTEGER PRIMARY KEY , name CHAR(32), email VARCHAR(40) );
The above code will create an id column and an email column in the database with values that are identical to that in table ‘table_name’. Here is an example where it would be more accurate to say that this would be like joining two tables together:
CREATE TABLE table_name ( id INTEGER PRIMARY KEY , name CHAR(32), email VARCHAR(40) ); ADD COLUMN table_name ( id INTEGER PRIMARY KEY , name CHAR(32), email VARCHAR(40) );
The above code will do exactly what it says it will do, but if you want to join two tables together you will need to use ORACLE’s PL/SQL commands or other DML commands such as INSERT … INTO… . The obvious alternative is to use this syntax:
CREATE TABLE table_name ( id INTEGER PRIMARY KEY , name CHAR(32), email VARCHAR(40) ); DELETE FROM table_name WHERE email = ?; ADD COLUMN table_name ( id INTEGER PRIMARY KEY , name CHAR(32), email VARCHAR(40) );
This query does not join two tables together because it doesn’t make sense for either one of them to have a primary key. It simply adds a new column called “email” and assigns it the value “?” which means not null — you cannot assign NULL values directly into sql variables, so if there were two users whose emails were both ? then they would not be joined together. Instead, they would both have two columns with NULL values in them. Using PL/SQL syntax also means that if your project uses Oracle 10g then any ID columns used by your tables will no longer exist — but hey, it
How to define a primary key in MYSQL?
A primary key is a column with a different name in the field used by the table to identify which row belongs to that particular user. A user can have many different columns with the same name, which are called secondary keys. The primary key is returned when you query your table, and it is also used by other functions of MySQL to identify the rows in your table. In other words, the primary key is basically a unique identifier for each row in your database.
There are two related but very different ways of using a primary key: directly and indirectly
Directly, you can use it as an identifier to uniquely identify each row in a table (and you can do this on both sides of the table). The difference between direct and indirect identifiers is that direct identifiers are specific to one side of the table whereas indirect identifiers can be used across both sides of the table.
If you have an index on some column (say id_user) then you could use it directly as an identifier for each row in a given user record in your database (as long as it’s unique across all users). If you want to refer to an id_user column from another place within your database i.e. for another query as an identifier for each row in that user record then you’ll need to use one of two ways:
- 1) An indirect identifier that refers back to an index on some column (this would be recommended if possible since it avoids having duplicate entries)
- 2) An indirect identifier that refers back to some other column within that index before going up through all of the rows in that index 3) An indirect identifier that refers back directly up through most or all rows (and potentially down all rows if not enough indexes exist on your columns).
If you want only one way or another of referring back at any given user record within your database then make sure there’s at least one way or another over which they can be referred with just their id_user reference value or else they will need indexes on those tables as well. Otherwise, chances are high they won’t be able to find them when querying them because there’s not enough information about them for them to know what their id_user reference value means at any given time.
How does MySQL internally determine which ID is linked from which other ID? It uses several heuristics: 1.) A user’s id_user is based off of his username, so if he has completely different
It’s a very common mistake to think that because your product is “different”, it must be a primary key. That’s simply wrong. There may be an added value in your product that is different from the existing ones, but that is not the main value of your product (or anything else).
The main thing is to get your product right.