No Primary Key
Level: INFO
Rationale
Tables in a relational database should ideally have a key that uniquely identifies a row within that table. Tables lacking a primary key is often considered poor design, as it can lead to data anomalies, complicate data relationships, and degrade query performance.
What is a Primary Key?
A primary key is a single column or a set of columns that uniquely identifies each row in a table.
Primary keys are important because they enable:
- Uniqueness and Integrity: Ensures that each row in the table is unique and identifiable.
- Performance: The database automatically creates an index for the primary key, improving query performance when retrieving or manipulating data based on the primary key.
- Relationships: Unique keys, like primary keys, are a prerequisite for defining foreign keys in other tables, which are critical for relational database design and efficient joins.
How to Resolve
For a table that lacks a primary key, the resolution involves identifying a column (or a set of columns) that can uniquely identify each row and altering the table to designate those columns as the primary key.
Given a table:
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If we assume id
is unique for each customer, we can add a primary key constraint to the table using:
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If no single column can serve as a unique identifier, consider using a composite key. A composite key combines multiple columns to form a unique identifier for each row.
Example:
Consider a table event_log that logs user activities without a primary key:
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To resolve the lack of a primary key and ensure that each log entry is uniquely identifiable, we can add a composite primary key on user_id and event_time:
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Ensure every table has a primary key, even if it's a synthetic key that doesn't have a natural counterpart in the data model.
When possible, use a simple fixed size types like int
, bigint
, and uuid
as the primary key for maximum efficiency.