SQL Server table index columns order -

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Will I create a column index when I use columns in different order?

What is the difference between the id, isValid, created and ID, created, isValid indices?

There is a difference in the order of asking more questions? 

  where id = 123 and isValid = 1 were created & lt; Getdate ()   
 versus  
  where id = 123 was created & lt; Getdate () and isValid = 1   
 column type: id  [int] , isValid  [bit] , created  [Datetime] )   
 
 
 
 Really enter  id, isValid, < / Code> and  id, created, isValid  index is created?   
  If you always use your  all three  columns  WHERE  section - there is no difference.  
 ( As Martin Smith explains in his comment - the parity is not examined since the benchmark,  does  case ) / P> 
 However: If only N left-most columns (here: n between 1 and 3) are used then only one index can be used  
 So if you have Is a query that only uses  id  and  isValid  for queries, then the first index can be  Is  used - but the second will be used to ensure  never .  
 And if you have questions that use the  ID  and  created  as their  WHERE  parameter, Then your second index can be used  probably , but can never be used before.

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