T-SQL - Overview
In 1970's the product called 'SEQUEL', structured English query language, developed by IBM and later SEQUEL was renamed to 'SQL' which stands for Structured Query Language.
In 1986, SQL was approved by ANSI (American national Standards Institute) and in 1987, it was approved by ISO (International Standards Organization).
SQL is a structure query language which is a common database language for all RDBMS products. Different RDBMS product vendors have developed their own database language by extending SQL for their own RDBMS products.
T-SQL stands for Transact Structure Query Language which is a Microsoft product and is an extension of SQL Language.
MS SQL Server - SQL\T-SQL
ORACLE - SQL\PL-SQL