When we give SELECT * FROM EMP; How does oracle respond?
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Answer Posted / umashankar
1.The PARSER scans/reads the SELECT statement and splits it
into some logical units such.
i.e: keywords/reserved word, operators, expressions and
identifiers.
2. SEQUENCE TREE or QUERY TREE is built the logical steps
needed to transform the source data into the format as
needed by the end result.
3. The QUERY OPRIMIZER analyzes the query in various ways
and selects the series of steps that returns the end
results fastest way. The query tree is updated to record
this exact series of steps. The final, optimized version of
the query tree is called the execution plan.
4. The RELATIONAL ENGINE starts executing the execution
plan which was prepared by the Query Optimizer.
5.The RELATIONAL ENGINE requests the STORAGE ENGINE pass up
data from the rowsets requested.
6. The RELATIONAL ENGINE processes the data (returns all
column values from EMP table) returned from the storage
engine to the client.
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