10.4 Query Optimization in Oracle
Oracle query processing begins with a parsing phase, which consists of syntax and semantic checking as described earlier, as well as a check of the shared pool area, a library that holds code for previously parsed SQL statements. If the statement is syntactically identical to one in the shared pool, Oracle does a semantic check to determine whether the statements have the same meaning. For example, two users may give the same name to tables that are actually different objects. In that case, SELECT statements for their tables may use the same syntax, but they refer to different tables, so they do not match semantically. Other environmental factors such as session settings can also cause a mismatch. If the statements ...
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