The From Clause

Information retrieval is an integral component of any database management system. Temporal database management systems should offer user-friendly and powerful means of retrieval of data according to temporal criteria. The From clause is an important component of the Select statement: it identifies the underlying relations from which the information is to be retrieved and allows the declaration of range variables. While variables merely serve as “correlation names” (e.g. for joining a table with itself) in SQL-92, TSQL2 variables are designed to increase the temporal expressiveness of the language, in addition to provide “syntactic sugar” in making some queries easier to formulate.