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Use LIKE instead of SUBSTRING

  
      

      
Continents

      

      Country   
      Continent 
      

      

      India
      Asia
      

      

      USA
      N.America 
      

      

      Italy
      Europe
      

      

    
 ----  Low Performance by using SUBSTRING 

      SELECT * FROM Continents
      WHERE SUBSTRING(Country,1,1) = 'I'


      
 ----  High Performance by using LIKE 

      SELECT * FROM Continents
      WHERE Country LIKE 'I%'
      
      
 ----  both Queries will give the same output but Performance is different, if the data is tooooo big 

    
      

      
Output

      

      Country   
      Continent 
      

      

      India
      Asia
      

      

      Italy
      Europe