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sqloracle-databasejoininner-join

Performing Inner Join for Multiple Columns in the Same Table


I have a scenario which I'm a bit stuck on. Let's say I have a survey about colors, and I have one table for the color data, and another for people's answers.

tbColors

color_code , color_name
     1     , 'blue'
     2     , 'green'
     3     , 'yellow'
     4     , 'red'

tbAnswers

answer_id  ,  favorite_color   ,   least_favorite_color   ,  color_im_allergic_to
    1      ,         1          ,         2                            3  
    2      ,         3          ,         1                            4
    3      ,         1          ,         1                            2
    4      ,         2          ,         3                            4

For display I want to write a SELECT that presents the answers table but using the color_name column from tbColors.

I understand the "most stupid" way to do it: naming tbColors three times in the FROM section, using a different alias for each column to replace.

How would a non-stupid way look?


Solution

  • This seems like the way to go:

    SELECT
      A.answer_id
      ,C1.color_name AS favorite_color_name
      ,C2.color_name AS least_favorite_color_name
      ,C3.color_name AS color_im_allergic_to_name
    FROM tbAnswers AS A
    INNER JOIN tbColors AS C1
      ON A.favorite_color = C1.color_code
    INNER JOIN tbColors AS C2
      ON A.least_favorite_color = C2.color_code
    INNER JOIN tbColors AS C3
      ON A.color_im_allergic_to = C3.color_code
    

    Rather than "stupid", I'd venture that this is a pretty standard query. This also presumes that all columns will have a valid value. Otherwise, replace all INNER JOINs with LEFT JOINs