Pořadí dotazu

Improving Query Performance in SQL Server

Dean Smith

Founder, Atamai Analytics

Dotaz na velká zemětřesení

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
...	...	...

Syntaktické pořadí

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

Syntaktické pořadí

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

Syntaktické pořadí

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

Syntaktické pořadí

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

Pořadí zpracování

                                 -- 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

Pořadí zpracování

                                 -- 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

Pořadí zpracování

                                 -- 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

Pořadí zpracování

                                 -- 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

Chyby zpracování


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

Zpracování 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'.

Zpracování 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'.

Zpracování 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'.

Zpracování 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'.

Bez chyb

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
...	...	...

Logické pořadí zpracování

1.  FROM

2.  ON

3.  JOIN

4.  WHERE

5.  GROUP BY

6.  HAVING


7.  SELECT


8.  DISTINCT

9.  ORDER BY

10. TOP

Lass uns üben!

Improving Query Performance in SQL Server