Python Generate A Unique Key

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Summary: in this tutorial, you will learn how to use the MySQL UNIQUE index to prevent duplicate values in one or more columns in a table.

Summary: in this tutorial, you will learn how to use SQLite PRIMARY KEY constraint to define a primary key for a table. Introduction to SQLite primary key. A primary key is a column or group of columns used to identify the uniqueness of rows in a table.
What is the best way to generate a unique key for the contents of a dictionary. My intention is to store each dictionary in a document store along with a unique id or hash so that I don't have to load the whole dictionary from the store to check if it exists already or not.
The secrets module is used for generating cryptographically strong random numbers suitable for managing data such as passwords, account authentication, security tokens, and related secrets. In particularly, secrets should be used in preference to the default pseudo-random number generator in the random module, which is designed for modelling and simulation, not security.
Although I can use this class to generate unique number in some sense but it is also not collision less. Moreover while generating key we can make key more complicated by making it as alpha numeric rather than numeric only. So, I used this class along with some character masking to generate unique key of fixed length. Below is code sample.

Introduction to the MySQL `UNIQUE` index

Use cryptography!pycrypto is not in active development anymore and if possible you should be using cryptography. Since June it's possible to generate SSH public keys as well: from cryptography.hazmat.primitives import serialization as cryptoserialization from cryptography.hazmat.primitives.asymmetric import rsa from cryptography.hazmat.backends. Random numbers¶. The secrets module provides access to the most secure source of randomness that your operating system provides. Class secrets.SystemRandom¶. A class for generating random numbers using the highest-quality sources provided by the operating system. How to generate a secret key with Python. GitHub Gist: instantly share code, notes, and snippets.

To enforce the uniqueness value of one or more columns, you often use the PRIMARY KEY constraint. However, each table can have only one primary key. Hence, if you want to have a more than one column or a set of columns with unique values, you cannot use the primary key constraint.

Luckily, MySQL provides another kind of index called UNIQUE index that allows you to enforce the uniqueness of values in one or more columns. Unlike the PRIMARY KEY index, you can have more than one UNIQUE index per table.

To create a UNIQUE index, you use the CREATE UNIQUE INDEX statement as follows:

Another way to enforce the uniqueness of value in one or more columns is to use the UNIQUE constraint.

When you create a UNIQUE constraint, MySQL creates a UNIQUE index behind the scenes.

The following statement illustrates how to create a unique constraint when you create a table.

/microsoft-office-365-activation-key-generator.html. In this statement, you can also use the UNIQUE INDEX instead of the UNIQUE KEY because they are synonyms.

If you want to add a unique constraint to an existing table, you can use the ALTER TABLE statement as follows:

MySQL `UNIQUE` Index & `NULL`

Unlike other database systems, MySQL considers NULL values as distinct values. Therefore, you can have multiple NULL values in the UNIQUE index.

This is how MySQL was designed. It is not a bug even though it was reported as a bug.

Another important point is that the UNIQUE constraint does not apply to NULL values except for the BDB storage engine.

MySQL `UNIQUE` index examples

Suppose, you want to manage contacts in an application. You also want that email of every contact in the contacts table must be unique.

To enforce this rule, you create a unique constraint in the CREATE TABLE statement as follows:

If you use the SHOW INDEXES statement, you will see that MySQL created a UNIQUE index for email column.

Let’s insert a row into the contacts table.

Now if you try to insert a row whose email is john.doe@mysqltutorial.org, you will get an error message.

Suppose you want the combination of first_name, last_name, and phone is also unique among contacts. In this case, you use the CREATE INDEX statement to create a UNIQUE index for those columns as follows:

Adding the following row into the contacts table causes an error because the combination of the first_name, last_name, and phone already exists.

In this tutorial, you have learned how to use the MySQL UNIQUE index to prevent duplicate values in the database.

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Unique keys add a layer of data integrity to an Azure Cosmos container. You create a unique key policy when you create an Azure Cosmos container. With unique keys, you make sure that one or more values within a logical partition is unique. You also can guarantee uniqueness per partition key.

After you create a container with a unique key policy, the creation of a new or an update of an existing item resulting in a duplicate within a logical partition is prevented, as specified by the unique key constraint. The partition key combined with the unique key guarantees the uniqueness of an item within the scope of the container.

For example, consider an Azure Cosmos container with email address as the unique key constraint and CompanyID as the partition key. When you configure the user's email address with a unique key, each item has a unique email address within a given CompanyID. Two items can't be created with duplicate email addresses and with the same partition key value.

To create items with the same email address, but not the same first name, last name, and email address, add more paths to the unique key policy. Instead of creating a unique key based on the email address only, you also can create a unique key with a combination of the first name, last name, and email address. This key is known as a composite unique key. In this case, each unique combination of the three values within a given CompanyID is allowed.

For example, the container can contain items with the following values, where each item honors the unique key constraint.

CompanyID	First name	Last name	Email address
Contoso	Gaby	Duperre	gaby@contoso.com
Contoso	Gaby	Duperre	gaby@fabrikam.com
Fabrikam	Gaby	Duperre	gaby@fabrikam.com
Fabrikam	Ivan	Duperre	gaby@fabrikam.com
Fabrkam	Duperre	gaby@fabraikam.com
Fabrkam	gaby@fabraikam.com

If you attempt to insert another item with the combinations listed in the previous table, you receive an error. The error indicates that the unique key constraint wasn't met. You receive either Resource with specified ID or name already exists or Resource with specified ID, name, or unique index already exists as a return message.

Define a unique key

You can define unique keys only when you create an Azure Cosmos container. A unique key is scoped to a logical partition. In the previous example, if you partition the container based on the ZIP code, you end up with duplicated items in each logical partition. Consider the following properties when you create unique keys:

You can't update an existing container to use a different unique key. In other words, after a container is created with a unique key policy, the policy can't be changed.
To set a unique key for an existing container, create a new container with the unique key constraint. Use the appropriate data migration tool to move the data from the existing container to the new container. For SQL containers, use the Data Migration tool to move data. For MongoDB containers, use mongoimport.exe or mongorestore.exe to move data.
A unique key policy can have a maximum of 16 path values. For example, the values can be /firstName, /lastName, and /address/zipCode. Each unique key policy can have a maximum of 10 unique key constraints or combinations. The combined paths for each unique index constraint must not exceed 60 bytes. In the previous example, first name, last name, and email address together are one constraint. This constraint uses 3 out of the 16 possible paths.
When a container has a unique key policy, Request Unit (RU) charges to create, update, and delete an item are slightly higher.
Sparse unique keys are not supported. If some unique path values are missing, they're treated as null values, which take part in the uniqueness constraint. For this reason, there can be only a single item with a null value to satisfy this constraint.
Unique key names are case-sensitive. For example, consider a container with the unique key constraint set to /address/zipcode. If your data has a field named ZipCode, Azure Cosmos DB inserts 'null' as the unique key because zipcode isn't the same as ZipCode. Because of this case sensitivity, all other records with ZipCode can't be inserted because the duplicate 'null' violates the unique key constraint.

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