Logical Query Processing Phases

This section introduces the phases involved in the logical processing of a query. I’ll first briefly describe each step. Then, in the following sections, I’ll describe the steps in much more detail and apply them to a sample query. You can use this section as a quick reference whenever you need to recall the order and general meaning of the different phases.

Example 1-1 contains a general form of a query, along with step numbers assigned according to the order in which the different clauses are logically processed.

Example 1-1. Logical query processing step numbers

(5) SELECT (5-2) DISTINCT (5-3) TOP(<top_specification>) (5-1) <select_list>
(1) FROM (1-J) <left_table> <join_type> JOIN <right_table> ON <on_predicate> ...

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