3. From relational algebra to SQL

There are two types of relational database manipulation language: procedural and assertional. A procedural language is one in which a query is expressed through a sequence of operations. This category includes graphical languages such as QBE (Query By Example), implemented in DBMS such as Access, as well as the algebraic language studied in this section. On the other hand, an assertional language is one in which a query contains the expression of the desired result. The latter category includes SQL (Structured Query Language ).

The aim of 3 is to study these two types of language. In the first...