Sql server 14 – primary key – youtube

We’ve discussed primary keys numerous times throughout this series, but this video is going to be devoted to going over primary keys in more detail and cover all parts of them. Data recovery miami Rather than a piece here and there, you can eat the whole pizza!

A primary key is a column that every table in your database is going to need. H2 database viewer The goal of a primary key is to force every row to be uniquely identifiable. Database replication It is a way to identify each row. Database record In order for this to work though, there are a few qualifications that are needed for a column to be a primary key.

First, every row has to have a primary key. Data recovery certification That means that the PK column cannot be null.

Database programs The second is that every row has to have a unique primary key. Raid 1 data recovery That means that the primary key column has to be labeled UNIQUE. Database 2016 You can essentially think of a primary key as the combination of the NOT NULL constraint and the UNIQUE constraint and you can only have one per table.

Lastly, the primary key should never change. Key value database There is a way to force this in our database that we will talk about shortly. Database mirroring But think about the reasoning. Data recovery techniques If a primary key changes, it is hard to tell whether it is the same entity with a new key, or a new entity. Data recovery using linux You might think, well, obviously it is the same entity with a new key because the data for the entity is exactly the same, but if we are following the conventions on primary keys, we know they shouldn’t change. Data recovery apple If we know that a key shouldn’t change, and it does, our thoughts are likely that there is a new entity.

Now, there are two types of primary keys. Data recovery google store Surrogate keys and natural keys. Database works Surrogate keys are computer generated and mean nothing outside of the database. Data recovery cheap Natural keys are when we use data that is real to uniquely define something. Database of state incentives for renewables and efficiency Each have their benefits. Data recovery usb stick The benefit of surrogate keys is that they automatically meet all qualifications for a primary key. Database companies The downside to surrogate keys is that it makes reading data a lot harder. Database application The benefit of natural keys is that it makes data easier to read, but it can be a challenge to find data that is going to be UNIQUE, NOT NULL, and never change.

Now how do you tell SQL Server that you want to create a primary key. Database online You have to use the PRIMARY KEY keywords for this column when you are creating the table. Database high availability We’ll be making primary keys when we get to the CREATE TABLE statement, but for now understand that you have to explicitly tell SQL Server that a column is a primary key.

If you are using surrogate keys, every row is going to need to have a unique value for this column. Database utility The easiest way to do this is to just count upwards. Data recovery zagreb The downside is that every time you insert data you are going to have to know what number to use. Database javascript Fortunately, there is an easier way, with what is known as an IDENTITY column. Database administrator jobs An identity column is a column in a table that automatically counts upwards. Data recovery for iphone If we set the PK column as the identity column, we do not have to worry about keeping track of the numbers we’ve already used. Data recovery victoria bc Now, you can only have one identity column per table, and you can only have one primary key per table. 10k database It makes sense to make the primary key column the identity column, but you can create any other column as the identity column, but you can only have one. Data recovery software mac In addition to the IDENTITY being useful for keeping things UNIQUE and NOT NULL, it is also useful for making sure values never change. Cost of data recovery from hard drive In fact, SQL Server is not going to let you update the values of an IDENTITY column.

It is important to understand that the concept of surrogate and natural keys is foreign to the database. S cerevisiae database The database does not care what kind of key you use, as long as the qualifications are met. Snl database There are no keywords that say surrogate. Database 4500 There are no keywords that say natural. Data recovery miami fl These are categories that we’ve made to help us better communicate about primary keys.