mysql - Should I also index columns included in a PRIMARY KEY? -


This question suddenly went into my head ... I have a table which, based on their ID, I create table looks like this: 

  create table 'ticket_content' (`ticket_ID` INT not tap, 'entity_id' INT not zero, 'indicated DO 'INT NO FAL DEFAULT 0, Primary key (`Ticket_ID`,` unit_ID`), key `ticket_id` (` ticket_ID`), key `unit_id` (` entity_id`))

I I am wondering if there is a need to include those previous two key lines, will I get better speed with the following questions, or do the individual columns automatically under the primary key Will be indexed from? 

  SELECT * ticket_contact WHERE ticket_id = 1; SELECT * ticket from ticket_contact WHERE entity_id = 1; The index created by    
 
 
  primary key  is identical to any Other (potential mixed)  UNIQUE  index therefore you do not need to create a separate index for  ticket_id  because it is in  (ticket_id, entity_id)  index The main column is included in the form. 
 
 By using that column independently of  ticket_id  
  
> you usually  entity_id

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