15.04.2020

Auto Generate Surrogate Key In Sql Server

Auto Generate Surrogate Key In Sql Server 7,0/10 3367 votes

Surrogate Key Sql Server
Database Surrogate Key
Surrogate Key Example
Create Table Surrogate Key Sql

Jun 24, 2012 A surrogate key is an auto generated value, usually integer, in the dimension table. It is made the primary key of the table and is used to join a dimension to a fact table. Among other benefits, surrogate keys allow you to maintain history in a dimension table. Aug 14, 2009 How do I create a Surrogate Key using a SQL Server Stmt/Function/What?? Hi folks, I'm loading a slowly changing dimension table and I need to be able to create a surrogate key. Is there a function or a statement I can call to create this surrogate key? Do I have to create.

Primary Key Generation Using Oracle's Sequence

Oracle provides the sequence utility to automatically generate unique primary keys. To use this utility to auto-generate primary keys for a CMP entity bean, you must create a sequence table and use the @AutomaticKeyGeneration annotation to point to this table.

In your Oracle database, you must create a sequence table that will create the primary keys, as shown in the following example:

This creates a sequences of primary key values, starting with 1, followed by 2, 3, and so forth. The sequence table in the example uses the default increment 1, but you can change this by specifying the increment keyword, such as increment by 3. When you do the latter, you must specify the exact same value in the cacheSize attribute of the @AutomaticKeyGeneration annotation:

If you have specified automatic table creation in the CMP bean's project settings, the sequence table will be created automatically when the entity bean is deployed. For more information, see @JarSettings Annotation. For more information on the definition of a CMP entity bean, see below.

Primary Key Generation Using SQL Server's IDENTITY

In SQL Server you can use the IDENTITY keyword to indicate that a primary-key needs to be auto-generated. The following example shows a common scenario where the first primary key value is 1, and the increment is 1:

In the CMP entity bean definition you need to specify SQLServer(2000) as the type of automatic key generator you are using. You can also provide a cache size:

Primary Key Generation Using a Named Sequence Table

A named sequence table is similar to the Oracle sequence functionality in that a dedicated table is used to generate primary keys. However, the named sequence table approach is vendor-neutral. To auto-generate primary keys this way, create a named sequence table using the two SQL statements shown in the example:

In the CMP entity bean definition you need to specify the named sequence table as the type of automatic key generator you are using. You can also provide a cache size:

Note. When you specify a cacheSize value for a named sequence table, a series of unique values are reserved for entity bean creation. When a new cache is necessary, a second series of unique values is reserved, under the assumption that the first series of unique values was entirely used. This guarantees that primary key values are always unique, although it leaves open the possibility that primary key values are not necessarily sequential. For instance, when the first series of values is 10..20, the second series of values is 21-30, even if not all values in the first series were actually used to create entity beans.

Defining the CMP Entity Bean

When defining a CMP entity bean that uses one of the primary key generators, you use the the @AutomaticKeyGeneration annotation to point to the name of the primary key generator table to obtain primary keys. Also, you must define a primary key field of type Integer or Long to set and get the auto-generated primary key. However, the ejbCreate method does not take a primary key value as an argument. Instead the EJB container adds the correct primary key to the entity bean record.

The following example shows what the entity bean might look like. Notice that the bean uses the named sequence option described above, and that ejbCreate method does not take a primary key:

What is a surrogate key

A surrogate key on a table is a column with a unique identifier for each row. The key is not generated from the table data. Data modelers like to create surrogate keys on their tables when they design data warehouse models. You can use the IDENTITY property to achieve this goal simply and effectively without affecting load performance.

Creating a table with an IDENTITY column

The IDENTITY property is designed to scale out across all the distributions in the Synapse SQL pool without affecting load performance. Therefore, the implementation of IDENTITY is oriented toward achieving these goals.

You can define a table as having the IDENTITY property when you first create the table by using syntax that is similar to the following statement:

You can then use INSERT.SELECT to populate the table.

This remainder of this section highlights the nuances of the implementation to help you understand them more fully.

Allocation of values

The IDENTITY property doesn't guarantee the order in which the surrogate values are allocated, which reflects the behavior of SQL Server and Azure SQL Database. However, in Synapse SQL pool, the absence of a guarantee is more pronounced.

The following example is an illustration:

In the preceding example, two rows landed in distribution 1. The first row has the surrogate value of 1 in column C1, and the second row has the surrogate value of 61. Both of these values were generated by the IDENTITY property. However, the allocation of the values is not contiguous. This behavior is by design.

Skewed data

The range of values for the data type are spread evenly across the distributions. If a distributed table suffers from skewed data, then the range of values available to the datatype can be exhausted prematurely. For example, if all the data ends up in a single distribution, then effectively the table has access to only one-sixtieth of the values of the data type. For this reason, the IDENTITY property is limited to INT and BIGINT data types only.

SELECT.INTO

When an existing IDENTITY column is selected into a new table, the new column inherits the IDENTITY property, unless one of the following conditions is true:

The SELECT statement contains a join.
Multiple SELECT statements are joined by using UNION.
The IDENTITY column is listed more than one time in the SELECT list.
The IDENTITY column is part of an expression.

If any one of these conditions is true, the column is created NOT NULL instead of inheriting the IDENTITY property.

CREATE TABLE AS SELECT

CREATE TABLE AS SELECT (CTAS) follows the same SQL Server behavior that's documented for SELECT.INTO. However, you can't specify an IDENTITY property in the column definition of the CREATE TABLE part of the statement. You also can't use the IDENTITY function in the SELECT part of the CTAS. To populate a table, you need to use CREATE TABLE to define the table followed by INSERT.SELECT to populate it. Photoshop cs5 product key generator free.

Explicitly inserting values into an IDENTITY column

Synapse SQL pool supports SET IDENTITY_INSERT <your table> ON OFF syntax. You can use this syntax to explicitly insert values into the IDENTITY column.

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Many data modelers like to use predefined negative values for certain rows in their dimensions. An example is the -1 or 'unknown member' row.

The next script shows how to explicitly add this row by using SET IDENTITY_INSERT:

Loading data

The presence of the IDENTITY property has some implications to yourt be used:

When the column data type is not INT or BIGINT
When the column is also the distribution key
When the table is an external table

The following related functions are not supported in Synapse SQL pool:

Common tasks

Surrogate Key Sql Server

This section provides some sample code you can use to perform common tasks when you work with IDENTITY columns.

Database Surrogate Key

Column C1 is the IDENTITY in all the following tasks.

Find the highest allocated value for a table

Surrogate Key Example

Use the MAX() function to determine the highest value allocated for a distributed table:

Find the seed and increment for the IDENTITY property

You can use the catalog views to discover the identity increment and seed configuration values for a table by using the following query:

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