How to get distinct values for non-key column fields in Laravel?

问题

This might be quite easy but have no idea how to.

I have a table that can have repeated values for a particular non-key column field. How do I write a SQL query using Query Builder or Eloquent that will fetch rows with distinct values for that column?

Note that I am not fetching that column only, it is in conjunction with other column values, so distinct() might not really work. So that question basically can be how to specify the column that I want to be distinct in a query now that distinct() accepts no parameters?

回答1:

You should use groupby. In Query Builder you can do it this way:

$users = DB::table('users')
            ->select('id','name', 'email')
            ->groupBy('name')
            ->get();

回答2:

In Eloquent you can also query like this:

$users = User::select('name')->distinct()->get();

回答3:

in eloquent you can use this

$users = User::select('name')->groupBy('name')->get()->toArray() ;

groupBy is actually fetching the distinct values, in fact the groupBy will categorize the same values, so that we can use aggregate functions on them. but in this scenario we have no aggregate functions, we are just selecting the value which will cause the result to have distinct values

回答4:

Though I am late to answer this, a better approach to get distinct records using Eloquent would be

$user_names = User::distinct()->get(['name']);

回答5:

Note that groupBy as used above won't work for postgres.

Using distinct is probably a better option - e.g. $users = User::query()->distinct()->get();

If you use query you can select all the columns as requested.

回答6:

$users = User::select('column1', 'column2', 'column3')->distinct()->get(); retrieves all three coulmns for distinct rows in the table. You can add as many columns as you wish.

回答7:

Grouping by will not work if the database rules don't allow any of the select fields to be outside of an aggregate function. Instead use the laravel collections.

$users = DB::table('users')
        ->select('id','name', 'email')
        ->get();

foreach($users->unique('name') as $user){
  //....
}

Someone pointed out that this may not be great on performance for large collections. I would recommend adding a key to the collection. The method to use is called keyBy. This is the simple method.

     $users = DB::table('users')
        ->select('id','name', 'email')
        ->get()
        ->keyBy('name');

The keyBy also allows you to add a call back function for more complex things...

     $users = DB::table('users')
        ->select('id','name', 'email')
        ->get()
        ->keyBy(function($user){
              return $user->name . '-' . $user->id;
         });

If you have to iterate over large collections, adding a key to it solve the performance issue.

回答8:

$users = Users::all()->unique('name');

回答9:

I found this method working quite well (for me) to produce a flat array of unique values:

$uniqueNames = User::select('name')->distinct()->pluck('name')->toArray();

If you ran ->toSql() on this query builder, you will see it generates a query like this:

select distinct `name` from `users`

The ->pluck() is handled by illuminate\collection lib (not via sql query).

回答10:

Tested for Laravel 5.8

Since you wanna get all columns from the table, you can collect all of the data and then filter it using Collections function called Unique

// Get all users with unique name
User::all()->unique('name')

// Get all & latest users with unique name 
User::latest()->get()->unique('name')

For more information you can check Laravel Collection Documentations

来源：https://stackoverflow.com/questions/25228823/how-to-get-distinct-values-for-non-key-column-fields-in-laravel

标签

laravel

eloquent

builder