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161 lines
4.4 KiB
Markdown
161 lines
4.4 KiB
Markdown
---
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slug: /en/engines/table-engines/integrations/mongodb
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sidebar_position: 135
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sidebar_label: MongoDB
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---
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# MongoDB
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MongoDB engine is read-only table engine which allows to read data from remote [MongoDB](https://www.mongodb.com/) collection.
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Only MongoDB v3.6+ servers are supported.
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**If you're facing troubles, please report the issue, and try to use [the legacy implementation](../../../operations/server-configuration-parameters/settings.md#use_legacy_mongodb_integration).
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Keep in mind that it is deprecated, and will be removed in next releases.**
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## Types mappings
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| MongoDB | ClickHouse |
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|--------------------|--------------------------------------------|
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| bool, int32, int64 | *any numeric type*, String |
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| int32 | Int32, String |
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| int64 | Int64, String |
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| double | Float64, String |
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| date | Date, Date32, DateTime, DateTime64, String |
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| string | String, UUID |
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| document | String(as JSON) |
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| array | Array, String(as JSON) |
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| oid | String |
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| *any other* | String |
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If key not found in MongoDB document, default value or null(if the column is nullable) will be inserted.
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## Supported clauses
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**You can disable all these restriction, see [mongodb_fail_on_query_build_error](../../../operations/settings/settings.md#mongodb_fail_on_query_build_error).**
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*Hint: you can use MongoDB table in CTE to perform any clauses, but be aware, that in some cases, performance will be significantly degraded.*
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### WHERE
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Only constant literals are allowed.
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PREWHERE and HAVING are not supported.
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### LIMIT and OFFSET
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Only `LIMIT` is supported.
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### ORDER BY
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Simple expressions only are supported, without any modification like COLLATE, WITH, TO, etc.
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### WINDOW
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Not supported.
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### GROUP BY
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Not supported.
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### Aggregation functions
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Not supported.
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## Notes
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### Situation with bool
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In ClickHouse `boolean` is an alias for `UInt8`, but in MongoDB it's a type.
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So, not in all cases it's possible to determine, is UInt8 supposed to be bool, and filters may not work correctly.
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But there is a hack: use `x = toBool(true)` instead of `x = true`.
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## Creating a Table {#creating-a-table}
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``` sql
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CREATE TABLE [IF NOT EXISTS] [db.]table_name
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(
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name1 [type1],
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name2 [type2],
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...
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) ENGINE = MongoDB(host:port, database, collection, user, password [, options]);
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```
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**Engine Parameters**
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- `host:port` — MongoDB server address.
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- `database` — Remote database name.
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- `collection` — Remote collection name.
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- `user` — MongoDB user.
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- `password` — User password.
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- `options` — MongoDB connection string options (optional parameter).
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:::tip
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If you are using the MongoDB Atlas cloud offering please add these options:
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```
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'connectTimeoutMS=10000&ssl=true&authSource=admin'
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```
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:::
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Also, you can simply pass a URI:
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``` sql
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ENGINE = MongoDB(uri, collection);
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```
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**Engine Parameters**
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- `uri` — MongoDB server's connection URI
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- `collection` — Remote collection name.
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## Usage Example {#usage-example}
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Create a table in ClickHouse which allows to read data from MongoDB collection:
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``` sql
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CREATE TABLE mongo_table
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(
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key UInt64,
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data String
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) ENGINE = MongoDB('mongo1:27017', 'test', 'simple_table', 'testuser', 'clickhouse');
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```
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or
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``` sql
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ENGINE = MongoDB('mongodb://testuser:clickhouse@mongo1:27017/test', 'simple_table');
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```
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To read from an SSL secured MongoDB server:
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``` sql
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CREATE TABLE mongo_table_ssl
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(
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key UInt64,
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data String
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) ENGINE = MongoDB('mongo2:27017', 'test', 'simple_table', 'testuser', 'clickhouse', 'ssl=true');
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```
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Query:
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``` sql
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SELECT COUNT() FROM mongo_table;
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```
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``` text
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┌─count()─┐
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│ 4 │
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└─────────┘
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```
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You can also adjust connection timeout:
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``` sql
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CREATE TABLE mongo_table
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(
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key UInt64,
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data String
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) ENGINE = MongoDB('mongo2:27017', 'test', 'simple_table', 'testuser', 'clickhouse', 'connectTimeoutMS=100000');
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```
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## Troubleshooting
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You can see the generated MongoDB query in DEBUG level logs.
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Implementation details can be found in [mongocxx](https://github.com/mongodb/mongo-cxx-driver) and [mongoc](https://github.com/mongodb/mongo-c-driver) documentations.
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