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Creating the key source. You can create the surrogate key source by adding a Surrogate Key Generator stage to a job by itself, with no input or output links. Deleting the key source. To delete the surrogate key source, design a job that uses a Surrogate Key Generator stage by itself, with no input or output links. Jul 20, 2016 There are three clear advantages that surrogate keys have: You know every table has one, and it probably has the same name everywhere: ID. It is relatively small (e.g. A BIGINT) You don’t have to go through the “hassle” of designing your table for 30 seconds longer, trying to find a natural key. Apr 20, 2006 The first problem is inherently caused by inserting meaningless data, and is always a problem, even with the built-in surrogate keys where the RDBMS provides a mechanism to retrieve the value. Sequences: a better surrogate key. Surrogate keys are often considered very bad practice, for a variety of good reasons I won’t discuss here. How I Defined a Time Dimension Using a Surrogate Key. The usage of surrogate keys is a general acceptable practice in DWH modelling. Time dimension (or better a calendar dimension as the considered granularity is a day) seems to be no exception to this rule. In practice in most cases it turns out that the time dimension.

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.
A better solution would be to use a second scrypt hash as your data encryption key, with a surrogate key to facilitate easy password changes: Generate two salts (s1 and s2) and store them in plaintext. Generate a cryptographically secure random key k - this is our surrogate key.

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Recommendations and examples for using the IDENTITY property to create surrogate keys on tables in Synapse SQL pool.

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.

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.

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:

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Common tasks

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

Column C1 is the IDENTITY in all the following tasks.