MongoDB: db.collection.distinct() method

Last update on November 21 2024 13:10:23 (UTC/GMT +8 hours)

db.collection.dataSize

The db.collection.distinct() method is used to find the distinct values for a specified field across a single collection and returns the results in an array.

Syntax:

db.collection.distinct(field, query)

Parameters:

Name	Description	Required / Optional	Type
field	The field for which to return distinct values.	Required	string
query	A query that specifies the documents from which to retrieve the distinct values.	Required	document

Sample document in the restaurants collection:


{
  "address": {
     "building": "1007",
     "coord": [ -73.856077, 40.848447 ],
     "street": "Morris Park Ave",
     "zipcode": "10462"
  },
  "borough": "Bronx",
  "cuisine": "Bakery",
  "grades": [
     { "date": { "$date": 1393804800000 }, "grade": "A", "score": 2 },
     { "date": { "$date": 1378857600000 }, "grade": "A", "score": 6 },
     { "date": { "$date": 1358985600000 }, "grade": "A", "score": 10 },
     { "date": { "$date": 1322006400000 }, "grade": "A", "score": 9 },
     { "date": { "$date": 1299715200000 }, "grade": "B", "score": 14 }
  ],
  "name": "Morris Park Bake Shop",
  "restaurant_id": "30075445"
}
............

Example: Return Distinct Values for a Field

The following example returns the distinct values for the field cuisine from all documents in the restaurants collection:

db.restaurants.distinct( "cuisine" );

Output:

The method returns the following array of distinct cuisine values:

[
        "Irish",
        "Bakery",
        "American ",
        "Hamburgers",
        "Jewish/Kosher",
        "Delicatessen",
        "Ice Cream, Gelato, Yogurt, Ices",
        "Chinese",
        "Other",
        "Chicken",
        "Turkish",
        "Caribbean",
        "Donuts",
        "Sandwiches/Salads/Mixed Buffet",
        "Bagels/Pretzels",
        "Pizza",
        "Italian",
        "Steak",
        "Continental",
        "Latin (Cuban, Dominican, Puerto Rican, South & Central American)",
        "Polish",
        "German",
        "French",
        "Pizza/Italian",
        "Mexican",
        "Spanish",
        "Café/Coffee/Tea",
        "Tex-Mex",
        "Pancakes/Waffles",
        "Soul Food",
        "Seafood",
        "Hotdogs",
        "Greek",
        "Not Listed/Not Applicable",
        "African",
        "Japanese",
        "Indian",
        "Armenian",
        "Thai",
        "Chinese/Cuban",
        "Mediterranean",
        "Korean",
        "Bottled beverages, including water, sodas, juices, etc.",
        "Russian",
        "Eastern European",
        "Middle Eastern",
        "Asian",
        "Ethiopian",
        "Vegetarian",
        "Barbecue",
        "Egyptian",
        "English",
        "Sandwiches",
        "Portuguese",
        "Indonesian",
        "Chinese/Japanese",
        "Filipino",
        "Juice, Smoothies, Fruit Salads",
        "Brazilian",
        "Afghan",
        "Vietnamese/Cambodian/Malaysia",
        "CafÃ©/Coffee/Tea",
        "Soups & Sandwiches",
        "Tapas",
        "Moroccan",
        "Pakistani",
        "Peruvian",
        "Bangladeshi",
        "Czech",
        "Salads",
        "Creole",
        "Fruits/Vegetables",
        "Iranian",
        "Cajun",
        "Scandinavian",
        "Polynesian",
        "Soups",
        "Australian",
        "Hotdogs/Pretzels",
        "Southwestern",
        "Nuts/Confectionary",
        "Hawaiian",
        "Creole/Cajun",
        "Californian",
        "Chilean"
]

Example: Return Distinct Values for an Embedded Field

The following example returns the distinct values for the field zipcode, embedded in the address field, from all documents in the restaurants collection:

db.restaurants.distinct( "address.zipcode" );

Output:

The method returns the following array of distinct zipcode values:

Example: Specify Query with distinct

The following example returns the distinct values for the field zipcode, embedded in the address field, from the documents whose cuisine is equal to "Delicatessen":

db.restaurants.distinct( "address.zipcode" , { "cuisine" : "Delicatessen" } );

Output:

The method returns the following array of distinct zipcode values:

Retrieve the restaurants data from here

Behavior

Array Fields

If the value of the specified field is an array, db.collection.distinct() considers each element of the array as a separate value.

For instance, if a field has as its value [ 1, [1], 1 ], then db.collection.distinct() considers 1, [1], and 1 as separate values.

Index Use

When possible, db.collection.distinct() operations can use indexes.

Indexes can also cover db.collection.distinct() operations.

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