70-461 Training Kit Chapter 1, Lesson 2: Logical Query Processing Phase

I think this is one the most import concept to master when learning SQL.

Keyed-in order: the syntax order
SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY

Logical Query Processing (with easy to remember phrase, credit to my co-worker): the order logically query is processed
FROM           -- For
WHERE        -- Wives
GROUP BY   -- Good
HAVING        -- Husbands
SELECT        -- Sing
ORDER BY   -- Often

Logical Query Processing detail
   FROM
Operators: CROSS JOIN, INNER JOIN, OUTER JOIN, CROSS APPLY, OUTER APPLY, PIVOT, UNPIVOT        
  WHERE    
  GROUP BY  
  HAVING      
SELECT
EXPRESSION
DISTINCT  
TOP    
ORDER BY  

Each phase output is served as input for the next phase
For optimization, SQL Server may process the query in any order.

Different between WHERE and HAVING clause:
WHERE evaluated before rows are grouped.
HAVING evaluated after rows are grouped.

SELECT statement:
All-at-once manner, no left to right
That mean this query will fail
SELECT 2*4 AS x, 2*x AS [2x]; --error invalid column x

ORDER BY
Returns a cursor, result is not a set and not relational
Add cost to query

Credits: Microsoft 70-461 Training Kit