ORACLE SQL Query Order of Operations

How ORACLE process the SQL Query? What is SQL Query Logical Processing Order?

Consider below Query clauses and understand how they get processed when executed in a form of a SQL Query:

FROM

JOINs

GROUP by

HAVING

WHERE

SELECT

ORDER BY

So, calculated SELECT columns or alias will not be available in the WHERE clause, but they will be available in the ORDER BY clause. Because the SELECT clause executed right before hand, everything from the SELECT should be available at the time of ORDER BY execution.

Also, SELECT columns are not referenceable  in the WHERE clause. If you create a column in the SELECT directive. It will not be available in the WHERE clause because the SELECT clause has not even been executed at the time the WHERE clause is being run.

When we pass, a SELECT query it executes under some phases. That includes

1) Checking by Server Process - Which type of Query is this - Sql or Pl/sql.
2) If sql - server process puts the code in sql area available under library cache under shared pool.
3) If pl/sql - server process puts the sql code in sql area and pl code in pl area available under library cache area under shared pool.
4) Now Parsing (Syntax, Privileges on user passing the query checks)
5) Check if execution plan is already available or not.
6) if not creates a execution plan on behalf of available statistics, if yes, uses available execution plan.
7) checks if the data blocks contains required data are available in buffer cache or not.
8) if yes, server process pick the data from BC and return to the user. If not server process reads the data blocks from data files and put the data blocks into buffer cache and return to the user.