Ordinea interogărilor

Îmbunătățirea performanței interogărilor în SQL Server

Dean Smith

Founder, Atamai Analytics

Interogare cutremure mari

SELECT Country, Place, Magnitude
FROM Earthquakes
WHERE Magnitude >= 9
ORDER BY Magnitude DESC;

Country	Place	Magnitude
CL	Bio-Bio; Chile	9.5
US	Southern Alaska	9.2
ID	off the west coast of northern Sumatra	9.1
JP	near the east coast of Honshu; Japan	9.1
...	...	...

Ordinea sintaxei

                                 -- Syntax Order
SELECT Country, Place, Magnitude -- 1. SELECT
FROM Earthquakes                                            
WHERE Magnitude >= 9            
ORDER BY Magnitude DESC;

Ordinea sintaxei

                                 -- Syntax Order
SELECT Country, Place, Magnitude -- 1. SELECT
FROM Earthquakes                 -- 2. FROM                            
WHERE Magnitude >= 9            
ORDER BY Magnitude DESC;

Ordinea sintaxei

                                 -- Syntax Order
SELECT Country, Place, Magnitude -- 1. SELECT
FROM Earthquakes                 -- 2. FROM                            
WHERE Magnitude >= 9             -- 3. WHERE
ORDER BY Magnitude DESC;

Ordinea sintaxei

                                 -- Syntax Order
SELECT Country, Place, Magnitude -- 1. SELECT
FROM Earthquakes                 -- 2. FROM                            
WHERE Magnitude >= 9             -- 3. WHERE
ORDER BY Magnitude DESC;         -- 4. ORDER BY

Ordinea procesării

                                 -- Syntax Order | Processing Order
SELECT Country, Place, Magnitude -- 1. SELECT        
FROM Earthquakes                 -- 2. FROM        1. FROM                       
WHERE Magnitude >= 9             -- 3. WHERE
ORDER BY Magnitude DESC;         -- 4. ORDER BY

Ordinea procesării

                                 -- Syntax Order | Processing Order
SELECT Country, Place, Magnitude -- 1. SELECT        
FROM Earthquakes                 -- 2. FROM        1. FROM                       
WHERE Magnitude >= 9             -- 3. WHERE       2. WHERE
ORDER BY Magnitude DESC;         -- 4. ORDER BY

Ordinea procesării

                                 -- Syntax Order | Processing Order
SELECT Country, Place, Magnitude -- 1. SELECT      3. SELECT
FROM Earthquakes                 -- 2. FROM        1. FROM                       
WHERE Magnitude >= 9             -- 3. WHERE       2. WHERE
ORDER BY Magnitude DESC;         -- 4. ORDER BY

Ordinea procesării

                                 -- Syntax Order | Processing Order
SELECT Country, Place, Magnitude -- 1. SELECT      3. SELECT
FROM Earthquakes                 -- 2. FROM        1. FROM                       
WHERE Magnitude >= 9             -- 3. WHERE       2. WHERE
ORDER BY Magnitude DESC;         -- 4. ORDER BY    4. ORDER BY

Erori de procesare


SELECT Country, 
       PlaceName, 
       Magnitude
FROM LargeEarthquakes            
WHERE Strength >= 9                 
ORDER BY Magnitud DESC;

Procesarea FROM

                        -- Processing Order
SELECT Country, 
       PlaceName, 
       Magnitude
FROM LargeEarthquakes   -- 1. FROM - table LargeEarthquakes does not exist
WHERE Strength >= 9                 
ORDER BY Magnitud DESC;

--------------------------------------------------------------------------------
-- ERROR
Invalid object name 'LargeEarthquakes'.

Procesarea WHERE

                        -- Processing Order
SELECT Country, 
       PlaceName, 
       Magnitude
FROM Earthquakes                              
WHERE Strength >= 9     -- 2. WHERE - column Strength does not exist 
ORDER BY Magnitud DESC;

--------------------------------------------------------------------------------
-- ERROR
Invalid column name 'Strength'.

Procesarea SELECT

                        -- Processing Order
SELECT Country, 
       PlaceName,       -- 3. SELECT - column PlaceName does not exist
       Magnitude 
FROM Earthquakes                              
WHERE Magnitude >= 9                 
ORDER BY Magnitud DESC;

--------------------------------------------------------------------------------
-- ERROR
Invalid column name 'PlaceName'.

Procesarea ORDER BY

                        -- Processing Order
SELECT Country, 
       Place, 
       Magnitude
FROM Earthquakes                              
WHERE Magnitude >= 9                 
ORDER BY Magnitud DESC;-- 4. ORDER BY - column misspelling

________________________________________________________

-- ERROR
Invalid column name 'Magnitud'.

Fără erori

SELECT Country, 
       Place, 
       Magnitude   
FROM Earthquakes                
WHERE Magnitude >= 9      
ORDER BY Magnitude DESC;

Country	Place	Magnitude
CL	Bio-Bio; Chile	9.5
US	Southern Alaska	9.2
ID	off the west coast of northern Sumatra	9.1
JP	near the east coast of Honshu; Japan	9.1
...	...	...

Ordinea logică de procesare

1.  FROM

2.  ON

3.  JOIN

4.  WHERE

5.  GROUP BY

6.  HAVING


7.  SELECT


8.  DISTINCT

9.  ORDER BY

10. TOP

Să exersăm!

Îmbunătățirea performanței interogărilor în SQL Server