The table below gives an overview of primary key support and enforcement in some of the major data warehouses. Enforcement: If a database enforces primary keys, that means it would raise an error if one of the constraints on primary keys (uniqueness and non-null) was broken during an INSERT or UPDATE statement.This will happen in the DDL (data definition language) to create the table, like in the example below, or an ALTER statement that specifies which field is the primary key. Support: If a primary key is supported in a database, that means they allow you to explicitly let the system know if a specific field is a primary key.What do we mean when we say a primary key is supported in a database? What does it mean if primary keys are enforced? Data warehouse support for primary keys The surrogate_key macro offers a DRY (don’t repeat yourself) solution to creating surrogate keys across different data warehouses in the event that your data doesn’t contain natural keys. One of these packages, dbt_utils, contains a series of macros that are built to alleviate common struggles in data modeling. ‘62aef884fbe3470ce7d9a92140b09b17’).ĭbt supports packages, libraries of open-source macros and data models, to help data teams avoid doing duplicative work. Surrogate keys, on the other hand, are usually alphanumeric strings since they are hashed values (ex. You can derive a surrogate key by hashing the date and ad_id fields to create a unique value per row.Ī note on primary key data types: natural keys will often take the form of an integer or other numeric value (ex. An example of this could be a custom table that reports daily performance per ad_id from an ad platform. You’ll essentially need to make a surrogate key in every table that lacks a natural key. A surrogate key is a hashed value of multiple fields in a dataset that create a uniqueness constraint on that dataset. In a perfect world, all of our primary keys would be natural keys… but this is an imperfect world! You can use documentation like entity relationship diagrams (ERDs) to help understand natural keys in APIs or tables. Perhaps in tables there’s a unique id field in each table that would act as the natural key. A natural key is a primary key that is innate to the data.Primary keys can be established two ways: naturally or derived through the data in a surrogate key. Use this glossary page to understand the importance of primary keys, how natural keys and surrogate keys differ, and how data warehouse support for primary keys varies. These two reasons coupled together can create a sense of distrust in the data and data team. Without primary keys that are tested for non-nullness and uniqueness, duplicate or null records can slip undetected into your data models and cause counts to be incorrect. Having a primary key in each data model is pretty much the one rule you can’t break. You have the flexibility to create the models and columns that are applicable to your business and the SQL you use to accomplish that is pretty much up to you and your team. One of the great things about data modeling is that there are very few rules to it. Establish a consistent naming system for primary keys across your data models.Ensure a lack of duplicate rows in your tables.It’s important to note that for each table or view in your database, there must only be one primary key column per database object.Īt their core, you create and use these row-level unique identifiers to: Primary keys take the form of a natural or surrogate key. A primary key is a non-null column in a database object that uniquely identifies each row.
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