Unique key constraints in Azure Cosmos DB.; 3 minutes to read +6; In this article. 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. At the first glance it seems to be satisfied Unique key as its using current time and hashing to generate key but GetHashCode doesn’t procduce unique code everytime. Althought Microsoft is using Double Hashing algorithms with N Number of collision resolving double hash function but during my experimentation I found lot of collisions.
Apr 20, 2006 How to Generate Sequences and Surrogate Keys in Generic SQL. Which uniquely identifies every row in the table and is “more minimal” than the inherently unique aspect of the data. The usual choice is a monotonically increasing integer, which is small and easy to use in foreign keys. It’s possible to generate the value in SQL, but it.
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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 | [email protected] |
| Contoso | Gaby | Duperre | [email protected] |
| Fabrikam | Gaby | Duperre | [email protected] |
| Fabrikam | Ivan | Duperre | [email protected] |
| Fabrkam | Duperre | [email protected] | |
| Fabrkam | [email protected] |
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 namedZipCode, Azure Cosmos DB inserts 'null' as the unique key becausezipcodeisn't the same asZipCode. Because of this case sensitivity, all other records with ZipCode can't be inserted because the duplicate 'null' violates the unique key constraint.
Next steps
- Learn more about logical partitions
- Explore how to define unique keys when creating a container
This topic describes how to create a unique index on a table in SQL Server 2019 (15.x) by using SQL Server Management Studio or Transact-SQL. A unique index guarantees that the index key contains no duplicate values and therefore every row in the table is in some way unique. There are no significant differences between creating a UNIQUE constraint and creating a unique index that is independent of a constraint. Data validation occurs in the same manner, and the query optimizer does not differentiate between a unique index created by a constraint or manually created. However, creating a UNIQUE constraint on the column makes the objective of the index clear. For more information on UNIQUE constraints, see Unique Constraints and Check Constraints.
Generate Random Key Sql Server
When you create a unique index, you can set an option to ignore duplicate keys. If this option is set to Yes and you attempt to create duplicate keys by adding data that affects multiple rows (with the INSERT statement), the row containing a duplicate is not added. If it is set to No, the entire insert operation fails and all the data is rolled back.
Note
You cannot create a unique index on a single column if that column contains NULL in more than one row. Similarly, you cannot create a unique index on multiple columns if the combination of columns contains NULL in more than one row. These are treated as duplicate values for indexing purposes.
In This Topic
Before you begin:
To create a unique index on a table, using:
Before You Begin
Benefits of a Unique Index
Multicolumn unique indexes guarantee that each combination of values in the index key is unique. For example, if a unique index is created on a combination of LastName, FirstName, and MiddleName columns, no two rows in the table could have the same combination of values for these columns.
Provided that the data in each column is unique, you can create both a unique clustered index and multiple unique nonclustered indexes on the same table.
Unique indexes ensure the data integrity of the defined columns.
Unique indexes provide additional information helpful to the query optimizer that can produce more efficient execution plans.
Typical Implementations
Unique indexes are implemented in the following ways:
PRIMARY KEY or UNIQUE constraint
When you create a PRIMARY KEY constraint, a unique clustered index on the column or columns is automatically created if a clustered index on the table does not already exist and you do not specify a unique nonclustered index. The primary key column cannot allow NULL values.
When you create a UNIQUE constraint, a unique nonclustered index is created to enforce a UNIQUE constraint by default. You can specify a unique clustered index if a clustered index on the table does not already exist.
For more information, see Unique Constraints and Check Constraints and Primary and Foreign Key Constraints.
Index independent of a constraint
Multiple unique nonclustered indexes can be defined on a table.
For more information, see CREATE INDEX (Transact-SQL).
Indexed view
To create an indexed view, a unique clustered index is defined on one or more view columns. The view is executed and the result set is stored in the leaf level of the index in the same way table data is stored in a clustered index. For more information, see Create Indexed Views.
Limitations and Restrictions
A unique index, UNIQUE constraint, or PRIMARY KEY constraint cannot be created if duplicate key values exist in the data.
Generate secret key in NodeJS. GitHub Gist: instantly share code, notes, and snippets. Generate secret key in NodeJS. GitHub Gist: instantly share code, notes, and snippets. Skip to content. All gists Back to GitHub. Sign in Sign up Instantly share code, notes, and snippets. Dehamzah / generate. Oct 23, 2019 If you want to generate random tokens or API keys: Use uuid, specifically the uuid.v4 method. Avoid node-uuid - it's not the same package, and doesn't produce reliably secure random values. If you want to generate random numbers in a range: Use random-number-csprng. Is it OK to generate session secret(or any other secret keys) and store it in host server? Using the latter exposes my secret key to SCM. So I decided to generate random string and store it in the host file system. Browse other questions tagged node.js session secret-key.A unique nonclustered index can contain included nonkey columns. For more information, see Create Indexes with Included Columns.
Security
Permissions
Requires ALTER permission on the table or view. User must be a member of the sysadmin fixed server role or the db_ddladmin and db_owner fixed database roles.
Using SQL Server Management Studio
To create a unique index by using the Table Designer
In Object Explorer, expand the database that contains the table on which you want to create a unique index.
Expand the Tables folder.
Right-click the table on which you want to create a unique index and select Design.
On the Table Designer menu, select Indexes/Keys.
In the Indexes/Keys dialog box, click Add.
Select the new index in the Selected Primary/Unique Key or Index text box.
In the main grid, under (General), select Type and then choose Index from the list.
Select Columns, and then click the ellipsis (..).
In the Index Columns dialog box, under Column Name, select the columns you want to index. You can select up to 16 columns. For optimal performance, select only one or two columns per index. For each column you select, indicate whether the index arranges values of this column in ascending or descending order.
When all columns for the index are selected, click OK.
In the grid, under (General), select Is Unique and then choose Yes from the list.
Optional: In the main grid, under Table Designer, select Ignore Duplicate Keys and then choose Yes from the list. Do this if you want to ignore attempts to add data that would create a duplicate key in the unique index.
Click Close.
On the File menu, click Savetable_name.
Create a unique index by using Object Explorer
In Object Explorer, expand the database that contains the table on which you want to create a unique index.
Expand the Tables folder.
Expand the table on which you want to create a unique index.
Right-click the Indexes folder, point to New Index, and select Non-Clustered Index...
In the New Index dialog box, on the General page, enter the name of the new index in the Index name box.
Select the Unique check box.
Under Index key columns, click Add...
In the Select Columns fromtable_name dialog box, select the check box or check boxes of the table column or columns to be added to the unique index.
Click OK.
In the New Index dialog box, click OK.
Using Transact-SQL
To create a unique index on a table
In Object Explorer, connect to an instance of Database Engine.
On the Standard bar, click New Query.
Copy and paste the following example into the query window and click Execute.
For more information, see CREATE INDEX (Transact-SQL).