Azure SQL Database Ledger: Blockchain power in SQL

Ledger functionality adds tamper-evidence to Azure SQL. It cryptographically links blocks of transactions together (like a blockchain), creating an immutable history. If a DBA tries to modify a row in the history table directly, the cryptographic verification fails.

Creating a Ledger Table

CREATE TABLE dbo.Transactions
(
    TransactionId int PRIMARY KEY,
    Amount decimal(10,2)
)
WITH 
(
    SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.TransactionsHistory),
    LEDGER = ON
);

Verification

You can run a stored procedure to verify the integrity of the database against a digest stored in immutable storage (Azure Blob with WORM).

Key Takeaways

• Use for Financial, Healthcare, and Supply Chain systems where auditability is mandated.
• It is transparent to the application (just normal SQL inserts).