Transact-SQL (T-SQL) is a dialect of SQL used by Microsoft SQL Server and SAP's Sybase.
From SQL Server Books Online:
Transact-SQL is the language used to administer instances of the SQL Server Database Engine, to create and manage database objects, and to insert, retrieve, modify, and delete data.
Transact-SQL is an extension of the language defined in the SQL standards published by the International Standards Organization (ISO) and the American National Standards Institute (ANSI).
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