> ## Documentation Index > Fetch the complete documentation index at: https://private-7c7dfe99-mintlify-fbfa8bee.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. > MongoDB engine is read-only table engine which allows to read data from a remote collection. # MongoDB table engine MongoDB engine is read-only table engine which allows to read data from a remote [MongoDB](https://www.mongodb.com/) collection. Only MongoDB v3.6+ servers are supported. [Seed list(`mongodb+srv`)](https://www.mongodb.com/docs/manual/reference/glossary/#std-term-seed-list) is not yet supported.

Creating a table

```sql theme={null} CREATE TABLE [IF NOT EXISTS] [db.]table_name ( name1 [type1], name2 [type2], ... ) ENGINE = MongoDB(host:port, database, collection, user, password[, options[, oid_columns]]); ``` **Engine Parameters** | Parameter | Description | | ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `host:port` | MongoDB server address. | | `database` | Remote database name. | | `collection` | Remote collection name. | | `user` | MongoDB user. | | `password` | User password. | | `options` | Optional. MongoDB connection string [options](https://www.mongodb.com/docs/manual/reference/connection-string-options/#connection-options) as a URL formatted string. e.g. `'authSource=admin&ssl=true'` | | `oid_columns` | Comma-separated list of columns that should be treated as `oid` in the WHERE clause. `_id` by default. | If you are using the MongoDB Atlas cloud offering connection url can be obtained from 'Atlas SQL' option. Seed list(`mongodb**+srv**`) is not yet supported, but will be added in future releases. Alternatively, you can pass a URI: ```sql theme={null} ENGINE = MongoDB(uri, collection[, oid_columns]); ``` **Engine Parameters** | Parameter | Description | | ------------- | ------------------------------------------------------------------------------------------------------ | | `uri` | MongoDB server's connection URI. | | `collection` | Remote collection name. | | `oid_columns` | Comma-separated list of columns that should be treated as `oid` in the WHERE clause. `_id` by default. |

Types mappings

| MongoDB | ClickHouse | | ----------------------- | --------------------------------------------------------------------- | | bool, int32, int64 | *any numeric type except Decimals*, Boolean, String | | double | Float64, String | | date | Date, Date32, DateTime, DateTime64, String | | string | String, *any numeric type(except Decimals) if formatted correctly* | | document | String(as JSON) | | array | Array, String(as JSON) | | oid | String | | binary | String if in column, base64 encoded string if in an array or document | | uuid (binary subtype 4) | UUID | | *any other* | String | If key is not found in MongoDB document (for example, column name doesn't match), default value or `NULL` (if the column is nullable) will be inserted.

OID

If you want a `String` to be treated as `oid` in the WHERE clause, just put the column's name in the last argument of the table engine. This may be necessary when querying a record by the `_id` column, which by default has `oid` type in MongoDB. If the `_id` field in the table has other type, for example `uuid`, you need to specify empty `oid_columns`, otherwise the default value for this parameter `_id` is used. ```javascript theme={null} db.sample_oid.insertMany([ {"another_oid_column": ObjectId()}, ]); db.sample_oid.find(); [ { "_id": {"$oid": "67bf6cc44ebc466d33d42fb2"}, "another_oid_column": {"$oid": "67bf6cc40000000000ea41b1"} } ] ``` By default, only `_id` is treated as `oid` column. ```sql theme={null} CREATE TABLE sample_oid ( _id String, another_oid_column String ) ENGINE = MongoDB('mongodb://user:pass@host/db', 'sample_oid'); SELECT count() FROM sample_oid WHERE _id = '67bf6cc44ebc466d33d42fb2'; --will output 1. SELECT count() FROM sample_oid WHERE another_oid_column = '67bf6cc40000000000ea41b1'; --will output 0 ``` In this case the output will be `0`, because ClickHouse doesn't know that `another_oid_column` has `oid` type, so let's fix it: ```sql theme={null} CREATE TABLE sample_oid ( _id String, another_oid_column String ) ENGINE = MongoDB('mongodb://user:pass@host/db', 'sample_oid', '_id,another_oid_column'); -- or CREATE TABLE sample_oid ( _id String, another_oid_column String ) ENGINE = MongoDB('host', 'db', 'sample_oid', 'user', 'pass', '', '_id,another_oid_column'); SELECT count() FROM sample_oid WHERE another_oid_column = '67bf6cc40000000000ea41b1'; -- will output 1 now ```

Supported clauses

Only queries with simple expressions are supported (for example, `WHERE field = ORDER BY field2 LIMIT `). Such expressions are translated to MongoDB query language and executed on the server side. You can disable all these restriction, using [mongodb\_throw\_on\_unsupported\_query](/reference/settings/session-settings#mongodb_throw_on_unsupported_query). In that case ClickHouse tries to convert query on best effort basis, but it can lead to full table scan and processing on ClickHouse side. It's always better to explicitly set type of literal because Mongo requires strict typed filters.\ For example you want to filter by `Date`: ```sql theme={null} SELECT * FROM mongo_table WHERE date = '2024-01-01' ``` This will not work because Mongo will not cast string to `Date`, so you need to cast it manually: ```sql theme={null} SELECT * FROM mongo_table WHERE date = '2024-01-01'::Date OR date = toDate('2024-01-01') ``` This applied for `Date`, `Date32`, `DateTime`, `Bool`, `UUID`.

Usage example

Assuming MongoDB has [sample\_mflix](https://www.mongodb.com/docs/atlas/sample-data/sample-mflix) dataset loaded Create a table in ClickHouse which allows to read data from MongoDB collection: ```sql title="Query" theme={null} CREATE TABLE sample_mflix_table ( _id String, title String, plot String, genres Array(String), directors Array(String), writers Array(String), released Date, imdb String, year String ) ENGINE = MongoDB('mongodb://:@atlas-sql-6634be87cefd3876070caf96-98lxs.a.query.mongodb.net/sample_mflix?ssl=true&authSource=admin', 'movies'); ``` ```sql title="Query" theme={null} SELECT count() FROM sample_mflix_table ``` ```text title="Response" theme={null} ┌─count()─┐ 1. │ 21349 │ └─────────┘ ``` ```sql title="Query" theme={null} -- JSONExtractString cannot be pushed down to MongoDB SET mongodb_throw_on_unsupported_query = 0; -- Find all 'Back to the Future' sequels with rating > 7.5 SELECT title, plot, genres, directors, released FROM sample_mflix_table WHERE title IN ('Back to the Future', 'Back to the Future Part II', 'Back to the Future Part III') AND toFloat32(JSONExtractString(imdb, 'rating')) > 7.5 ORDER BY year FORMAT Vertical; ``` ```text title="Response" theme={null} Row 1: ────── title: Back to the Future plot: A young man is accidentally sent 30 years into the past in a time-traveling DeLorean invented by his friend, Dr. Emmett Brown, and must make sure his high-school-age parents unite in order to save his own existence. genres: ['Adventure','Comedy','Sci-Fi'] directors: ['Robert Zemeckis'] released: 1985-07-03 Row 2: ────── title: Back to the Future Part II plot: After visiting 2015, Marty McFly must repeat his visit to 1955 to prevent disastrous changes to 1985... without interfering with his first trip. genres: ['Action','Adventure','Comedy'] directors: ['Robert Zemeckis'] released: 1989-11-22 ``` ```sql title="Query" theme={null} -- Find top 3 movies based on Cormac McCarthy's books SELECT title, toFloat32(JSONExtractString(imdb, 'rating')) AS rating FROM sample_mflix_table WHERE arrayExists(x -> x LIKE 'Cormac McCarthy%', writers) ORDER BY rating DESC LIMIT 3; ``` ```text title="Response" theme={null} ┌─title──────────────────┬─rating─┐ 1. │ No Country for Old Men │ 8.1 │ 2. │ The Sunset Limited │ 7.4 │ 3. │ The Road │ 7.3 │ └────────────────────────┴────────┘ ```

Troubleshooting

You can see the generated MongoDB query in DEBUG level logs. Implementation details can be found in [mongocxx](https://github.com/mongodb/mongo-cxx-driver) and [mongoc](https://github.com/mongodb/mongo-c-driver) documentations.