SQLClient

SqlClient is the data provider for Microsoft SQL Server within the .NET ecosystem, implemented as part of ADO.NET. It enables applications to connect to SQL Server, execute commands, and read results, using a set of classes that map to SQL Server concepts such as connections, commands, readers, and transactions.

Key features include connection pooling, parameterized queries to prevent injection, and support for transactions, stored procedures, and bulk operations via the SqlBulkCopy class. The provider exposes core types such as SqlConnection, SqlCommand, SqlDataReader, SqlDataAdapter, and SqlTransaction, with mappings between SQL Server data types and .NET types. It also supports asynchronous operations (for example, OpenAsync and ExecuteReaderAsync) and, when enabled in the connection string, Multiple Active Result Sets (MARS).

Cross-platform and versions: In the early days of .NET Framework, System.Data.SqlClient served as the primary provider. With the advent of .NET Core and .NET 5+, Microsoft introduced Microsoft.Data.SqlClient as the modern, cross-platform provider, and it is the recommended option for new development. System.Data.SqlClient remains available for compatibility with legacy .NET Framework applications. Microsoft.Data.SqlClient is commonly updated to support newer SQL Server features and security requirements, including TLS updates and enterprise capabilities such as Always Encrypted in compatible environments.

Usage and scope: SqlClient is designed for direct SQL Server interaction from .NET languages and can be used in desktop, web, and service applications. It provides essential data access capabilities, with continued emphasis on performance, reliability, and security when interfacing with SQL Server.