ลำดับของคิวรี

การปรับปรุงประสิทธิภาพคิวรีใน SQL Server

Dean Smith

Founder, Atamai Analytics

คิวรีแผ่นดินไหวขนาดใหญ่

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
...	...	...

ลำดับ Syntax

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

ลำดับ Syntax

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

ลำดับ Syntax

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

ลำดับ Syntax

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

ลำดับการประมวลผล

                                 -- 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

ลำดับการประมวลผล

                                 -- 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

ลำดับการประมวลผล

                                 -- 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

ลำดับการประมวลผล

                                 -- 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

ข้อผิดพลาดในการประมวลผล


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

ประมวลผล 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'.

ประมวลผล 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'.

ประมวลผล 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'.

ประมวลผล 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'.

ไม่มีข้อผิดพลาด

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
...	...	...

ลำดับการประมวลผลเชิงตรรกะ

1.  FROM

2.  ON

3.  JOIN

4.  WHERE

5.  GROUP BY

6.  HAVING


7.  SELECT


8.  DISTINCT

9.  ORDER BY

10. TOP

มาฝึกกันเถอะ!

การปรับปรุงประสิทธิภาพคิวรีใน SQL Server