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description: In SQL Server, a differential backup captures only data that has changed since the last full backup, which is the base of the differential backup.
This backup and restore article is relevant for all [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] databases.
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This backup and restore article is relevant for all [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] databases.
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A differential backup is based on the most recent, previous full data backup. A differential backup captures only the data that has changed since that full backup. The full backup upon which a differential backup is based is known as the *base* of the differential. Full backups, except for copy-only backups, can serve as the base for a series of differential backups, including database backups, partial backups, and file backups. The base backup for a file differential backup can be contained within a full backup, a file backup, or a partial backup.
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@@ -36,7 +36,7 @@ The following illustration shows how a differential backup works. The figure sho
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:::image type="content" source="media/differential-backups-sql-server/how-differential-backups-work.png" alt-text="Diagram of how the differential bitmap identifies changed extents.":::
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> [!NOTE]
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> The differential bitmap is not updated by a copy-only backup. Therefore, a copy-only backup does not affect subsequent differential backups.
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> The differential bitmap isn't updated by a copy-only backup. Therefore, a copy-only backup doesn't affect subsequent differential backups.
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A differential backup that is taken fairly soon after its base can be significantly smaller than the differential base. This saves storage space and backup time. However, as a database changes over time, the difference between the database and a specific differential base increases. The longer the time between a differential backup and its base, the larger the differential backup is likely to be. This means that the differential backups can eventually approach the differential base in size. A large differential backup loses the advantages of a faster and smaller backup.
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## Differential backups of databases with memory-optimized tables
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For information about differential backups and databases with memory-optimized tables, see [Backing Up a Database with Memory-Optimized Tables](../../relational-databases/in-memory-oltp/backing-up-a-database-with-memory-optimized-tables.md).
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For information about differential backups and databases with memory-optimized tables, see [Backing Up a Database with Memory-Optimized Tables](../in-memory-oltp/backing-up-a-database-with-memory-optimized-tables.md).
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## Differential backups of read-only databases
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For read-only databases, full backups used alone are easier to manage than when they're used with differential backups. When a database is read-only, backup and other operations can't change the metadata that is contained in the file. Therefore, metadata that is required by a differential backup, such as the log sequence number at which the differential backup begins (the differential base LSN) is stored in the `master` database. If the differential base is taken when the database is read-only, the differential bitmap indicates more changes than have occurred since the base backup. The extra data is read by backup, but isn't written to the backup, because the `differential_base_lsn` stored in the [backupset](../../relational-databases/system-tables/backupset-transact-sql.md) system table is used to determine whether the data has changed since the base.
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For read-only databases, full backups used alone are easier to manage than when they're used with differential backups. When a database is read-only, backup and other operations can't change the metadata that is contained in the file. Therefore, metadata that is required by a differential backup, such as the log sequence number at which the differential backup begins (the differential base LSN) is stored in the `master` database. If the differential base is taken when the database is read-only, the differential bitmap indicates more changes than have occurred since the base backup. The extra data is read by backup, but isn't written to the backup, because the `differential_base_lsn` stored in the [backupset](../system-tables/backupset-transact-sql.md) system table is used to determine whether the data has changed since the base.
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When a read-only database is rebuilt, restored, or detached and attached, the differential-base information is lost. This occurs because the `master` database isn't synchronized with the user database. The [!INCLUDE[ssDEnoversion](../../includes/ssdenoversion-md.md)] can't detect or prevent this problem. Any later differential backups aren't based on the most recent full backup and could provide unexpected results. To establish a new differential base, we recommend that you create a full database backup.
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When a read-only database is rebuilt, restored, or detached and attached, the differential-base information is lost. This occurs because the `master` database isn't synchronized with the user database. The [!INCLUDE[ssDEnoversion](../../includes/ssdenoversion-md.md)] can't detect or prevent this problem. Any later differential backups aren't based on the most recent full backup and could provide unexpected results. To establish a new differential base, we recommend that you create a full database backup.
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### Best practices for using differential backups with a read-only database
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## Related tasks
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-[Create a Differential Database Backup (SQL Server)](../../relational-databases/backup-restore/create-a-differential-database-backup-sql-server.md)
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-[Create a Differential Database Backup (SQL Server)](create-a-differential-database-backup-sql-server.md)
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-[Restore a differential database backup (SQL Server)](restore-a-differential-database-backup-sql-server.md)
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-[Restore a Differential Database Backup (SQL Server)](../../relational-databases/backup-restore/restore-a-differential-database-backup-sql-server.md)
Copy file name to clipboardExpand all lines: docs/relational-databases/clr-integration-database-objects-types-net-framework/mapping-clr-parameter-data.md
description: This article lists Microsoft SQL Server data types, equivalents in the CLR for SQL Server, and native CLR equivalents in the .NET Framework.
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author: rwestMSFT
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ms.author: randolphwest
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ms.date: 12/27/2024
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ms.date: 07/15/2025
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ms.service: sql
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ms.subservice: clr
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ms.topic: "reference"
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The following table lists [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)] data types, their equivalents in the common language runtime (CLR) for [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)] in the `System.Data.SqlTypes` namespace, and their native CLR equivalents in the .NET Framework.
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| SQL Server data type | Type (in `System.Data.SqlTypes` or `Microsoft.SqlServer.Types`) | CLR data type (.NET Framework) |
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