SQL Server is a relational database management system that is based on the standard of the current SQL version. Microsoft SQL Server is available in various editions that cover a wide range of products. The editions differ mainly in terms of price, functions and hardware restrictions. The MSSQL server can also be used as a data warehouse, providing employees in a company with a view of the business and its data. Through its business intelligence platform, it provides a scalable infrastructure that enables IT to promote the use of business intelligence across the organization and deliver business intelligence where users want it. SQL Server consists of many services, such as Analysis Services, Reporting Services and Integration Services, and tools, such as SQL Server Data Tools (SSDT).
Microsoft SQL Server uses the SQL variant T-SQL (Transact-SQL) for database queries. T-SQL mainly adds additional syntax for use in stored procedures and transactions. MSSQL also supports OLE DB and ODBC (Open Database Connectivity).
Since SQL Server 2005 (code name "Yukon"), programming languages that run on the .NET CLR are supported for the creation of stored procedures. With Visual Studio, a suitable IDE has also been supplied since 2005.
 

Microsoft offers a range of techniques for storing data redundantly.
Clustering Replication Log Shipping Mirroring AlwaysOn Availability Groups AlwaysOn Failover Cluster Instance Introduction SQL Server 6.5 SQL Server 7.0 SQL Server 2000 SQL Server 2005 SQL Server 2012 SQL Server 2012 Minimum. License Standard / (Web) Enterprise: Peer-To-Peer Standard: Snapshot /Transactional / Merge Standard / (Web) Standard Enterprise Standard Max. Number of copies 15 unlimited unlimited 1 3 unlimited Additional infrastructure shared network resource (Distributor Server) Monitoring Server (Optional) Witness Server (Optional) - shared network resource Failover manual / automatic only manual manual only manual / automatic manual / automatic manual / automatic manual / automatic Designation Source Node Publisher Primary Principal Primary Node Designation Copy N...
 

It is now also possible to store SQL Server data files in Azure and host an SQL Server database on a virtual machine in Azure. Encryption of backups during the backup process using AES 128, AES 192, AES 256 and Triple DES has been added.
Support for failover cluster instances has been improved.

ESet up business-critical intelligent applications
The new SQL Server 2016 delivers breakthrough business-critical in-memory performance, real-time operational analytics, deeper insights into your data thanks to built-in advanced analytics and new rich visualizations on all mobile devices. It is the first database built in the cloud and it sets new standards for the speed of innovation. This hybrid cloud platform helps you build solutions that enable customers to complement their existing on-premise investments.
 

Depending on the version of Microsoft SQL Server, there are different editions of the product. The editions differ either in their range of functions or the maximum hardware support. For example, higher-value editions have access to more RAM or more processors, which means they offer more performance. The respective name of an edition indicates its intended use or purpose. For example, the most expensive version under SQL Server 2008, the Datacenter Edition, is used for large data centers, while the SQL Server Web Edition is intended specifically for web hosts or websites.
The following table lists an overview of different SQL Server versions and their available editions:
 

In contrast to the limitation of 128 GB in the Standard Edition Enterprise Edition allows you to fully utilize the maximum memory and the numerous processor cores of your host system.

The protocol layer implements the external interface to SQL Server. All operations that can be called on SQL Server are transferred to it via a Microsoft-defined format known as Tabular Data Stream (TDS). TDS is an application layer protocol used to transfer data between a database server and a client. Originally designed and developed by Sybase Inc. for their Sybase SQL Server relational database engine in 1984, and later by Microsoft in Microsoft SQL Server, TDS packets can be embedded in other physical transport-dependent protocols, including TCP/IP, named pipes and shared memory. Consequently, access to SQL Server is possible via these protocols. In addition, the SQL Server API is also available via web services. Data store
A data store is a database that is a collection of tables with typed columns. SQL Server supports various data types, including primitive types such as integer, float, decimal, char (including strings), varchar (variable-length strings), binary (for unstructured data blobs), text (for text data) and others. Rounding floating point numbers to integers uses either symmetric arithmetic rounding or symmetric rounding (fixed) depending on arguments: SELECT round (2.5, 0) returns 3.
 

SQL Server buffers pages in RAM to minimize disk I/O. Each 8 KB page can be buffered in memory, and the amount of all currently buffered pages is called the buffer cache. The amount of memory available to SQL Server determines how many pages are cached in memory. The buffer cache is managed by the buffer manager. Either reading from or writing to any page copies it to the buffer cache. Subsequent reads or writes are redirected to the in-memory copy and not to the on-disc version. The page is only updated by the buffer manager on the disk if the in-memory cache has not been referenced for some time. When writing pages back to disk, asynchronous I/O is used, with the I/O operation being performed in a background thread so that other operations do not have to wait for the I/O operation to complete. Each page is written together with its checksum when it is written. When the page is read, its checksum is recalculated and compared with the saved version to ensure that the page has not been corrupted or tampered with in the meantime. Concurrency and locking
SQL Server allows multiple clients to use the same database at the same time.
 

The main mode for retrieving data from a SQL Server database is querying. The query is expressed using a variant of SQL called T-SQL, a dialect that Microsoft SQL Server shares with Sybase SQL Server due to its legacy. The query declaratively specifies what is to be retrieved. It is processed by the query processor, which determines the sequence of steps required to retrieve the requested data. The sequence of actions required to execute a query is called a query plan. There may be several ways to process the same query. For a query that contains a join statement and a select statement, executing join on both tables and then executing select on the results will produce the same result as selecting from each table and then executing the join, but will result in a different execution plans. In this case, SQL Server selects the plan that is expected to deliver the results in the shortest possible time. This is called query optimization and is performed by the query processor itself.

SQL Server includes a cost-based query optimizer that attempts to optimize costs in terms of the resources required to execute the query.

T-SQL (Transact-SQL) is the secondary means of programming and managing SQL Server. It provides keywords for the operations that can be performed on SQL Server. These include creating and modifying database schemas, entering and editing data in the database, and monitoring and managing the server itself. Client applications that consume data or manage the server utilize SQL Server functionality by sending T-SQL queries and statements, which are then processed by the server and return results (or errors) to the client application. SQL Server enables administration with T-SQL. For this purpose, read-only tables are made available from which server statistics can be read. The management functionality is made available via system-defined stored procedures that can be called from T-SQL queries to perform the management operation. It is also possible to create linked servers using T-SQL. Linked servers allow a single query to process operations performed on multiple servers. Native SQL Server client
SQL Server Native Client is the native client-side data access library for Microsoft SQL Server from version 2005.
 

Microsoft SQL Server 2022 includes a component called SQL CLR ("Common Language Runtime") through which it is integrated with .NET Framework. Unlike most other applications that use .NET Framework, SQL Server itself hosts the .NET Framework runtime, i.e. memory, thread and resource management requirements of .NET Framework are fulfilled by SQLOS itself and not by the underlying Windows operating system. SQLOS provides deadlock detection and removal services for .NET code. With SQL CLR, stored procedures and triggers can be written in any managed .NET language, including C# and VB.NET. Managed code can also be used to define UDTs (user-defined types) that can persist in the database. The managed code is compiled into CLI assemblies and registered in the database after checking for type safety. They can then be called like any other procedure. However, only a subset of the base class library is available when code is executed under SQL CLR. Most APIs for the user interface functionality are not available.

Microsoft SQL Server 2019 includes a component called SQL CLR ("Common Language Runtime") through which it is integrated with .NET Framework. Unlike most other applications that use .NET Framework, SQL Server itself hosts the .NET Framework runtime, i.e. memory, thread and resource management requirements of .NET Framework are fulfilled by SQLOS itself and not by the underlying Windows operating system. SQLOS provides deadlock detection and removal services for .NET code. With SQL CLR, stored procedures and triggers can be written in any managed .NET language, including C# and VB.NET. Managed code can also be used to define UDTs (user-defined types) that can persist in the database. The managed code is compiled into CLI assemblies and registered in the database after checking for type safety. They can then be called like any other procedure. However, only a subset of the base class library is available when code is executed under SQL CLR. Most APIs for the user interface functionality are not available.