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Create and use updatable ledger tables

  • Článek

Applies to: SQL Server 2022 (16.x) Azure SQL Database Azure SQL Managed Instance

This article shows you how to create an updatable ledger table. Next, you'll insert values in your updatable ledger table and then make updates to the data. Finally, you'll view the results by using the ledger view. We'll use an example of a banking application that tracks banking customers' balances in their accounts. Our example will give you a practical look at the relationship between the updatable ledger table and its corresponding history table and ledger view.

Prerequisites

Create an updatable ledger table

We'll create an account balance table with the following schema.

Column name Data type Description
CustomerID int Customer ID - Primary key clustered
LastName varchar (50) Customer last name
FirstName varchar (50) Customer first name
Balance decimal (10,2) Account balance

  1. Use SQL Server Management Studio or Azure Data Studio to create a new schema and table called [Account].[Balance].

    CREATE SCHEMA [Account];
GO  
CREATE TABLE [Account].[Balance]
(
    [CustomerID] INT NOT NULL PRIMARY KEY CLUSTERED,
    [LastName] VARCHAR (50) NOT NULL,
    [FirstName] VARCHAR (50) NOT NULL,
    [Balance] DECIMAL (10,2) NOT NULL
)
WITH 
(
 SYSTEM_VERSIONING = ON (HISTORY_TABLE = [Account].[BalanceHistory]),
 LEDGER = ON
);

    Note

    Specifying the LEDGER = ON argument is optional if you enabled a ledger database when you created your database.

  2. When your updatable ledger table is created, the corresponding history table and ledger view are also created. Run the following T-SQL commands to see the new table and the new view.

    SELECT 
ts.[name] + '.' + t.[name] AS [ledger_table_name]
, hs.[name] + '.' + h.[name] AS [history_table_name]
, vs.[name] + '.' + v.[name] AS [ledger_view_name]
FROM sys.tables AS t
JOIN sys.tables AS h ON (h.[object_id] = t.[history_table_id])
JOIN sys.views v ON (v.[object_id] = t.[ledger_view_id])
JOIN sys.schemas ts ON (ts.[schema_id] = t.[schema_id])
JOIN sys.schemas hs ON (hs.[schema_id] = h.[schema_id])
JOIN sys.schemas vs ON (vs.[schema_id] = v.[schema_id])
WHERE t.[name] = 'Balance';

    Screenshot that shows querying new ledger tables.

  3. Insert the name Nick Jones as a new customer with an opening balance of $50.

    INSERT INTO [Account].[Balance]
VALUES (1, 'Jones', 'Nick', 50);

  4. Insert the names John Smith, Joe Smith, and Mary Michaels as new customers with opening balances of $500, $30, and $200, respectively.

    INSERT INTO [Account].[Balance]
VALUES (2, 'Smith', 'John', 500),
(3, 'Smith', 'Joe', 30),
(4, 'Michaels', 'Mary', 200);

  5. View the [Account].[Balance] updatable ledger table, and specify the GENERATED ALWAYS columns added to the table.

    SELECT [CustomerID]
   ,[LastName]
   ,[FirstName]
   ,[Balance]
   ,[ledger_start_transaction_id]
   ,[ledger_end_transaction_id]
   ,[ledger_start_sequence_number]
   ,[ledger_end_sequence_number]
 FROM [Account].[Balance];

    In the results window, you'll first see the values inserted by your T-SQL commands, along with the system metadata that's used for data lineage purposes.

    • The ledger_start_transaction_id column notes the unique transaction ID associated with the transaction that inserted the data. Because John, Joe, and Mary were inserted by using the same transaction, they share the same transaction ID.

    • The ledger_start_sequence_number column notes the order by which values were inserted by the transaction.

      Screenshot that shows ledger table example 1.

  6. Update Nick's balance from 50 to 100.

    UPDATE [Account].[Balance] SET [Balance] = 100
WHERE [CustomerID] = 1;

  7. View the [Account].[Balance] ledger view, along with the transaction ledger system view to identify users that made the changes.

     SELECT
 t.[commit_time] AS [CommitTime] 
 , t.[principal_name] AS [UserName]
 , l.[CustomerID]
 , l.[LastName]
 , l.[FirstName]
 , l.[Balance]
 , l.[ledger_operation_type_desc] AS Operation
 FROM [Account].[Balance_Ledger] l
 JOIN sys.database_ledger_transactions t
 ON t.transaction_id = l.ledger_transaction_id
 ORDER BY t.commit_time DESC;

    Tip

    We recommend that you query the history of changes through the ledger view and not the history table.

    Nick's account balance was successfully updated in the updatable ledger table to 100.
    The ledger view shows that updating the ledger table is a DELETE of the original row with 50. The balance with a corresponding INSERT of a new row with 100 shows the new balance for Nick.

    Screenshot that shows ledger table example 3.

Permissions

Creating updatable ledger tables requires the ENABLE LEDGER permission. For more information on permissions related to ledger tables, see Permissions.

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