- A Primary Key Can Be Computer Generated Video
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- A Primary Key Can Be Computer Generated
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A primary key uniquely defines a row on a table. Some primary keys can be described as a surrogate key as well. A primary key is called a surrogate key if the value was generated programatically (i.e. A DB trigger that generates a sequence). For instance, if you have a table called STUDENT with a primary key column studentid. It worked as expected. The following statement inserts a new row into the identitydemo table with a provided value for the id column. INSERT INTO identitydemo(id,description) VALUES (2, 'Oracle identity column example with GENERATED BY DEFAULT'). Mar 22, 2002 The great primary-key debate. Programmatically or system-generated keys are stable, they’re not subject to input errors, and they’re never null. They provide the perfect pointer to related.
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A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values.
A table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key.
If a table has a primary key defined on any field(s), then you cannot have two records having the same value of that field(s).
A Primary Key Can Be Computer Generated Video
Note − You would use these concepts while creating database tables.
Create Primary Key
Here is the syntax to define the ID attribute as a primary key in a CUSTOMERS table.
To create a PRIMARY KEY constraint on the 'ID' column when the CUSTOMERS table already exists, use the following SQL syntax −
NOTE − If you use the ALTER TABLE statement to add a primary key, the primary key column(s) should have already been declared to not contain NULL values (when the table was first created).
For defining a PRIMARY KEY constraint on multiple columns, use the SQL syntax given below.
To create a PRIMARY KEY constraint on the 'ID' and 'NAMES' columns when CUSTOMERS table already exists, use the following SQL syntax.
Delete Primary Key
You can clear the primary key constraints from the table with the syntax given below.
The Identity column is new to Oracle 12c, and this article explains what it is for and how to use it.
Have you ever needed to generate a unique value for a column, and have it automatically set when you insert a new value?
In other databases, this is simple, but in Oracle, it was a little complicated - until Oracle 12c.
The Problem
Let's say you wanted to have a unique value generated for a column, such as a primary key value. You wanted this value to be automatically generated when you insert a new record, without having to specify it.
If you've used other databases, such as MySQL, this was easy to do. You would just define a column as AUTO_INCREMENT, and whenever you insert a new record, you would leave this column out of the INSERT statement, and the new value would be automatically set.
A Primary Key Can Be Computer Generated Video
However, the only way to do this in Oracle is to use a combination of a sequence and a trigger on the table. (LINK)
Until Oracle 12c.
What is an Identity Column in Oracle?
Oracle 12c has introduced the concept of an IDENTITY column. You can set a column as an identity, which works in a similar way to the auto increment column.
Then, whenever you insert a new record into the table, you don't need to specify a value for this column, as it will be generated automatically.
It's a great way to ensure a value is always unique in a column, and to make sure that whoever inserts a record doesn't need to manually call a sequence.
3 Steps total
Step 1: Create table with an Identity column
To set up an identity column, you need to do it as part of the CREATE TABLE or ALTER TABLE statements.
For example:
CREATE TABLE idtest (
new_id NUMBER GENERATED AS IDENTITY,
first_name VARCHAR2(100)
last_name VARCHAR2(100)
);
This means that the new_id column is now an identity column.
If you want to set an existing column as an identity column, I would advise against it. It could cause issues with your data. The better way to do this would be to create a new table and use some renaming of tables to get this done.
Just like with a sequence, you can specify different values and parameters for an identity column.
Let's say you wanted to start your values at 1000, and increment by 5 every time. You can do this in your CREATE TABLE statement:
CREATE TABLE idtest2 (
new_id NUMBER GENERATED AS IDENTITY (START WITH 1000 INCREMENT BY 5)
testval VARCHAR2(50)
);
Whenever you insert new values, they will start at 1000 and go up by 5 (1000, 1005, 1010, 1015).
Step 2: Insert new records into the table
So, now you have set up the identity column, it's time to use it.
To use an identity column, you just run an INSERT statement that does not use this column.
INSERT INTO idtest (first_name, last_name) VALUES (‘Peter’, ‘Parker’);
INSERT INTO idtest (first_name, last_name) VALUES (‘Clark’, ‘Kent’);
INSERT INTO idtest (first_name, last_name) VALUES (‘Bruce’, ‘Wayne’);
A Primary Key Can Be Computer Generated Free
Each of these statements will insert a new value in the idtest table. Notice how I did not specify a value for the new_id column.
Step 3: Query table to see that values have been set
Now, to check that the values have been inserted, we can query the table.
SELECT new_id, first_name, last_name
FROM idtest;
You can see that the records exist and that the new_id has been set.
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References
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- The Full List - Oracle 12c New Features for Developers
