Rails select unique values from a column

Question

I already have a working solution  but I would really like to know why this doesn t work   ratings   Model select  rating  uniq ratings each    r  puts r rating     It selects  but don t print unique values  it prints all values  including the duplicates  And it s in the documentation  http   guides rubyonrails org active record querying html selecting-specific-fields

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If you want to also select extra fields   Model select  DISTINCT ON  models ratings  models ratings  models id   map    m   m id  m ratings

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If I am going right to way then    Current query   Model select  rating    is returning array of object and you have written query  Model select  rating  uniq   uniq is applied on array of object and each object have unique id  uniq is performing its job correctly because each object in array is uniq   There are many way to select distinct rating    Model select  distinct rating   map  amp  rating    or   Model select  distinct rating   collect  amp  rating    or  Model select  rating  map  amp  rating  uniq   or   Model select  name  collect  amp  rating  uniq   One more thing  first and second query   find distinct data by SQL query   These queries will considered  london  and  london  nbsp  nbsp   same means it will neglect to space  that s why it will select  london  one time in your query result   Third and forth query   find data by SQL query and for distinct data applied ruby uniq mehtod  these queries will considered  london  and  london     different  that s why it will select  london  and  london    both in your query result   please prefer to attached image for more understanding and have a look on  Toured   Awaiting RFP

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If you re going to use Model select  then you might as well just use DISTINCT  as it will return only the unique values  This is better because it means it returns less rows and should be slightly faster than returning a number of rows and then telling Rails to pick the unique values    Model select  DISTINCT rating     Of course  this is provided your database understands the DISTINCT keyword  and most should

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Model select  rating  uniq   This code works as  DISTINCT   not as Array uniq  since rails 3 2

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Model select  rating  distinct

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You can use the following Gem  active record distinct on Model distinct on  rating   Yields the following query  SELECT DISTINCT ON    quot models quot   quot rating quot     quot models quot    FROM  quot models quot

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If anyone is looking for the same with Mongoid  that is  Model distinct  rating

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Model pluck  quot DISTINCT column name quot

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Some answers don t take into account the OP wants a array of values  Other answers don t work well if your Model has thousands of records  That said  I think a good answer is       Model uniq select  ratings  map  amp  ratings        gt   SELECT DISTINCT ratings FROM  models       Because  first you generate a array of Model  with diminished size because of the select   then you extract the only attribute those selected models have  ratings

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Model uniq pluck  rating     SELECT DISTINCT  models   rating  FROM  models    This has the advantages of not using sql strings and not instantiating models

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Model select  rating   The result of this is a collection of Model objects  Not plain ratings  And from uniq s point of view  they are completely different  You can use this  Model select  rating  map  amp  rating  uniq  or this  most efficient   Model uniq pluck  rating   Rails 5  Model distinct pluck  rating   Update Apparently  as of rails 5 0 0 1  it works only on  quot top level quot  queries  like above  Doesn t work on collection proxies   quot has many quot  relations  for example   Address distinct pluck  city      gt    Moscow   user addresses distinct pluck  city      gt    Moscow    Moscow    Moscow    In this case  deduplicate after the query user addresses pluck  city  uniq     gt    Moscow

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This works too   Model pluck  DISTINCT rating

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Another way to collect uniq columns with sql   Model group  rating  pluck  rating

[ruby-on-rails] Rails: select unique values from a column

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