Key generation is the process of generating keys in cryptography. A key is used to encrypt and decrypt whatever data is being encrypted/decrypted. A device or program used to generate keys is called a key generator or keygen. 1 Generation in cryptography. A surrogate key (or synthetic key, entity identifier, system-generated key, database sequence number, factless key, technical key, or arbitrary unique identifier citation needed) in a database is a unique identifier for either an entity in the modeled world or an object in the database. Oct 11, 2006 Just recently I ran into a problem with what seems to be a deficiency in the Oracle Database. When trying to return an auto-generated key as is done in Microsoft's SQL database, it seems Oracle for whatever reason didn't add this capability, the key couldn't be passed back to the.Net call.
Summary: in this tutorial, you will learn how to use the
GENERATED AS IDENTITY
constraint to create the PostgreSQL identity column for a table.Introduction to PostgreSQL identity column
PostgreSQL version 10 introduced a new feature called
GENERATED AS IDENTITY
constraint that allows you to automatically assign a unique value to a column. The GENERATED AS IDENTITY
constraint is the SQL standard-conforming variant of the PostgreSQL’s SERIAL
column.The following illustrates the syntax of the
GENERATED AS IDENTITY
constraint:In this syntax:
- The type can be
SMALLINT
,INT
, orBIGINT
. - The
GENERATED ALWAYS
instructs PostgreSQL to always generate a value for the identity column. If you attempt to insert (or update) a value into theGENERATED ALWAYS AS IDENTITY
column, PostgreSQL will issue an error. - The
GENERATED BY DEFAULT
also instructs PostgreSQL to generate a value for the identity column. However, if you provide a value for insert or update, PostgreSQL will use that value to insert into the identity column instead of using the system-generated value.
PostgreSQL allows you to have more than one identity column in a table. Similar to the
SERIAL
constraint, the GENERATED AS IDENTITY
constraint also uses the SEQUENCE
object internally.PostgreSQL identity column examples
A
) GENERATED ALWAYS
example
First, create a table named
color
with the color_id
as the identity column:Second, insert a new row into the
color
table:Because
color_id
column has the GENERATED AS IDENTITY
constraint, PostgreSQL generates a value for it as shown in the query below:Third, insert a new row by providing values for both
color_id
and color_name
columns:PostgreSQL issued the following error:
To fix the error, in this case, you can use the
OVERRIDING SYSTEM VALUE
clause as follows:Or use
GENERATED BY DEFAULT AS IDENTITY
instead.B) GENERATED BY DEFAULT AS IDENTITY
example
First, drop the
color
table and recreate it. This time we use the GENERATED BY DEFAULT AS IDENTITY
instead:Second, insert a row into the
color
table:It works as expected.
Third, insert another row with a value for the
color_id
column:Unlike the previous example that uses the
GENERATED ALWAYS AS IDENTITY
constraint, this statement also works.C) Sequence options example
Because the
GENERATED AS IDENTITY
constraint uses the SEQUENCE
object, you can specify the sequence options for the system-generated values.For example, you can specify the starting value and the increment as follows:
In this example, the system-generated value for the
color_id
column starts with 10 and the increment value is also 10.First, insert a new row into the color table:
The starting value for
color_id
column is ten as shown below:Second, insert another row into the
color
table:The value for the
color_id
of the second row is 20 because of the increment option.Adding an identity column to an existing table
You can add identity columns to an existing table by using the following form of the
ALTER TABLE
statement:Let’s see the following example.
First, create a new table named
shape
:Second, change the
shape_id
column to an identity column:The following command describes the
shape
table in psql tool:It returns the following output which is what we expected:
Changing an identity column
You can change the characteristics of an existing identity column by using the following
ALTER TABLE
statement:For example, the following statement changes the
shape_id
column of the shape
table to GENERATED BY DEFAULT
:The following command describes the structure of the shape table in the psql tool:
As you can see from the output, the
shape_id
column changed from GENERATED ALWAYS
to GENERATED BY DEFAULT
.Removing the GENERATED AS IDENTITY constraint
The following statement removes the
GENERATED AS IDENTITY
constraint from an existing table:For example, you can remove the
GENERATED AS IDENTITY
constraint column from the shape_id
column of the shape
table as follows:In this tutorial, you have learned how to use the PostgreSQL identity column and how to manage it through the
GENERATED AS IDENTITY
constraint.On Windows, you can create SSH keys in many ways. This document explains how to use two SSH applications, PuTTY and Git Bash.
Joyent recommends RSA keys because the node-manta CLI programs work with RSA keys both locally and with the ssh agent. DSA keys will work only if the private key is on the same system as the CLI, and not password-protected.
PuTTY
PuTTY is an SSH client for Windows. You can use PuTTY to generate SSH keys. PuTTY is a free open-source terminal emulator that functions much like the Terminal application in macOS in a Windows environment. This section shows you how to manually generate and upload an SSH key when working with PuTTY in the Windows environment.
About PuTTY
PuTTY is an SSH client for Windows that you will use to generate your SSH keys. You can download PuTTY from www.chiark.greenend.org.uk.
When you install the PuTTY client, you also install the PuTTYgen utility. PuTTYgen is what you will use to generate your SSH key for a Windows VM.
This page gives you basic information about using PuTTY and PuTTYgen to log in to your provisioned machine. For more information on PuTTY, see the PuTTY documentation |
---|
Generating an SSH key
To generate an SSH key with PuTTYgen, follow these steps:
- Open the PuTTYgen program.
- For Type of key to generate, select SSH-2 RSA.
- Click the Generate button.
- Move your mouse in the area below the progress bar. When the progress bar is full, PuTTYgen generates your key pair.
- Type a passphrase in the Key passphrase field. Type the same passphrase in the Confirm passphrase field. You can use a key without a passphrase, but this is not recommended.
- Click the Save private key button to save the private key. You must save the private key. You will need it to connect to your machine.
- Right-click in the text field labeled Public key for pasting into OpenSSH authorized_keys file and choose Select All.
- Right-click again in the same text field and choose Copy.
Importing your SSH key
Now you must import the copied SSH key to the portal.
- After you copy the SSH key to the clipboard, return to your account page.
- Choose to Import Public Key and paste your SSH key into the Public Key field.
- In the Key Name field, provide a name for the key. Note: although providing a key name is optional, it is a best practice for ease of managing multiple SSH keys.
- Add the key. It will now appear in your table of keys under SSH.
PuTTY and OpenSSH use different formats of public SSH keys. If the text you pasted in the SSH Key starts with
—— BEGIN SSH2 PUBLIC KEY
, it is in the wrong format. Be sure to follow the instructions carefully. Your key should start with ssh-rsa AAAA…
.Once you upload your SSH key to the portal, you can connect to your virtual machine from Windows through a PuTTY session.
Git Bash
The Git installation package comes with SSH. Using Git Bash, which is the Git command line tool, you can generate SSH key pairs. Git Bash has an SSH client that enables you to connect to and interact with Triton containers on Windows.
To install Git:
- (Download and initiate the Git installer](https://git-scm.com/download/win).
- When prompted, accept the default components by clicking Next.
- Choose the default text editor. If you have Notepad++ installed, select Notepad++ and click Next.
- Select to Use Git from the Windows Command Prompt and click Next.
- Select to Use OpenSSL library and click Next.
- Select to Checkout Windows-style, commit Unix-style line endings and click Next.
- Select to Use MinTTY (The default terminal of mYSYS2) and click Next.
- Accept the default extra option configuration by clicking Install.
When the installation completes, you may need to restart Windows.
Launching GitBash
To open Git Bash, we recommend launching the application from the Windows command prompt:
- In Windows, press Start+R to launch the Run dialog.
- Type
C:Program FilesGitbinbash.exe
and press Enter.
Generating SSH keys
First, create the SSH directory and then generate the SSH key pair.
One assumption is that the Windows profile you are using is set up with administrative privileges. Given this, you will be creating the SSH directory at the root of your profile, for example:
When To Use System Generated Key West
- At the Git Bash command line, change into your root directory and type.
- Change into the .ssh directory
C:Usersjoetest.ssh
- To create the keys, type:
- When prompted for a password, type apassword to complete the process. When finished, the output looks similar to:
Uploading an SSH key
To upload the public SSH key to your Triton account:
- Open Triton Service portal, select Account to open the Account Summary page.
- From the SSH section, select Import Public Key.
- Enter a Key Name. Although naming a key is optional, labels are a best practice for managing multiple SSH keys.
- Add your public SSH key.
When To Use System Generated Key West
When Triton finishes the adding or uploading process, the public SSH key appears in the list of SSH keys.
What are my next steps?
- Adding SSH keys to agent.
- Set up the Triton CLI and CloudAPI on Windows.
- Set up the Triton CLI and CloudAPI.
- Create an instance in the Triton Service Portal.
- Set up the
triton-docker
command line tool. - Visit PuTTYgen to learn more about the PuTTYgen and to seethe complete installation and usage guide.