Transact-SQL (T-SQL) is an extension of SQL used by Microsoft SQL products and services, including Microsoft SQL Server, and by SAP Adaptive Server Enterprise (SAP ASE). Microsoft states that tools and applications communicating with a SQL Server database do so by sending T-SQL commands. SAP describes its implementation as an enhanced version of the relational database language.

History

In January 1988, Microsoft and Ashton-Tate announced Microsoft SQL Server, based on a relational database management system licensed from Sybase. Sybase Adaptive Server Enterprise was later renamed SAP Adaptive Server Enterprise. Microsoft and SAP publish separate Transact-SQL documentation for their respective database systems.

Microsoft implementation

The features described in this section refer to Microsoft's implementation of Transact-SQL.

Variables and control flow

Local variables begin with an at sign (@) and are declared using DECLARE. A newly declared variable has the value NULL. Values can be assigned using SET or SELECT, although Microsoft recommends SET for variable assignment.

Control-flow constructs include BEGIN...END, IF...ELSE, WHILE, BREAK, CONTINUE, RETURN, GOTO, WAITFOR, THROW, and TRY...CATCH.

Stored procedures and error handling

Stored procedures can accept input parameters, return values through output parameters, contain statements that operate on a database, and return a status value to their caller.

The TRY...CATCH construct transfers control to a CATCH block when certain execution errors occur inside its associated TRY block.

Data modification and bulk loading

Transact-SQL extends the DELETE statement with an additional FROM clause, allowing rows to be identified using joined table sources. Its UPDATE statement also accepts a FROM clause containing table, view, or derived-table sources used to determine which rows are updated.

The BULK INSERT statement imports data from a file into a table or view. Depending on the Microsoft database product, the source can be a file accessible to the server or a file in Azure Storage.

See also