Primary key or Unique index?

Surrogate keys and Natural keys

Regarding keys, we must differentiate between surrogate and natural. The former is a synthetic ID, often a sequential number generated by the database, used when a natural unique identifier doesn't exist. In contrast, the latter comes from inherent data, such as an ISBN for a book.

-- Because toll booth 001 is not the same as toll booth 002 
-- (especially when 002 is near a coffee shop).
ALTER TABLE TollBooths ADD CONSTRAINT PK_TollBooths PRIMARY KEY (BoothID);


-- Every car is unique, just like you!
ALTER TABLE Cars ADD CONSTRAINT PK_Cars PRIMARY KEY (VIN);


Transactional replication in SQL Server

If you're dealing with transactional replication, especially in MS SQL Server, then primary keys and unique constraints are your lifeline. They guarantee unique identification of each record during synchronization. Beware, you can't disable indexes related to the primary key without facing replication consequences.

Navigate many-to-many relationships

For many-to-many relationship tables, primary keys are indispensable. Skipping them can lead to data anomalies and a clusterfest of queries and joint operations.

-- When a book loves multiple authors and an author adores writing multiple books.
CREATE TABLE BookAuthors (
    BookID int REFERENCES Books (BookID),
    AuthorID int REFERENCES Authors (AuthorID),
    PRIMARY KEY (BookID, AuthorID)
);
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Effortless database design and management

Established coding standards guiding usage of primary keys and unique indexes are a boon in database maintenance and standardization. And, while using email as a unique identifier sounds practical, its mutable nature and duplication risk make it unreliable. After all, John might have more than one email!

Optimizing large-scale databases

Unique indexes can replace primary keys in large-scale databases where optimization becomes crucial. However, it calls for careful consideration of database design and replication strategy.

Consequences of absence of primary keys

Tables without primary keys can trigger editability issues in some applications and may fail to guarantee data integrity. Adhering to industry best practices when designing without primary keys is recommended.

Visual representation

Imagine entry into a castle:

🏰 Castle Entrance 🏰

The Primary Key is like the castle's main gate master key (🔐). There can only be ONE master key, and it uniquely identifies each visitor (row).

The Unique Index is like varying access cards (🎟️) for entering different castle doors. They're UNIQUE but not necessarily used for MAIN entry.

Recall, the Primary Key is the 🔐, whereas the Unique Index is the 🎟️.

Replicating tables without primary keys in MS SQL Server

Replicating tables without primary keys in MS SQL Server can be a touchy process, and needs deft attention to detail for maintaining data consistency.

The role of unique identification

Use Primary keys to uniquely identify records. A lack of unique identifiers can generate mind-bending data integrity issues.

Helpful reading and literature

Delving deeper into database design warrants reading specialized literature that dishes out wisdom on primary keys and unique indexes. Check your local technical journals, or rely on your favorite search engine.