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This document describes the basic concepts of the Procedural Query Language (PQL) of Odysseus, shows how to use and extend the language. In contrast to languages SQL based languages like the Continuous Query Language (CQL) or StreamSQL, PQL is more procedural and functional than declarative. The first part of this document is for users and shows how to formulate queries with PQL. The second part of the document is intended for developers who want to extend PQL.
Using PQL in Queries
PQL is an operator based language where an operator can be seen as a logical building block of the query. Thus, PQL is the connection of several operators. Since Odysseus differentiates between logical operators and their physical operators, which are the implementing counterpart, PQL is based upon logical operators. Therefore, it may happen that the query gets changed during the transformation from the logical query plan into the physical query plan. This includes also logical optimization techniques like the restructuring of the logical query plan. To avoid this, you can explicitly turn off the query optimization.
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