ClickHouse/docs/en/operations/table_engines/external_data.md
Ivan Blinkov 16ca492938
WIP on docs (#3813)
* CLICKHOUSE-4063: less manual html @ index.md

* CLICKHOUSE-4063: recommend markdown="1" in README.md

* CLICKHOUSE-4003: manually purge custom.css for now

* CLICKHOUSE-4064: expand <details> before any print (including to pdf)

* CLICKHOUSE-3927: rearrange interfaces/formats.md a bit

* CLICKHOUSE-3306: add few http headers

* Remove copy-paste introduced in #3392

* Hopefully better chinese fonts #3392

* get rid of tabs @ custom.css

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* Add jdbc.md to ToC and some translation, though it still looks badly incomplete

* minor punctuation

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* find . -name '*.md' -type f | xargs -I{} perl -pi -e 's//g' {}

* find . -name '*.md' -type f | xargs -I{} perl -pi -e 's/ sql/g' {}

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* Update some links on front page

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* Proper docs nav translation

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* fix docs build

* Update Amsterdam link

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* CLICKHOUSE-3751: stem terms while searching docs

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* More verbose 3rd party libs disclaimer

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* Separate third-party stuff in ToC too

* Update links

* Move stuff that is not really (only) a client library into a separate page

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* minor changes

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* Split third-party GUI to open-source and commercial

* Mention some RDBMS integrations + ad-hoc translation fixes

* Add rel="external nofollow" to outgoing links from docs

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* Apply suggestions by @sundy-li

* Mobile version of front page improvements

* test

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* Update LICENSE

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* Highlight current article as suggested by @sundy-li

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* Introduce backup.md (only "en" for now)

* Mention INSERT+SELECT in backup.md

* Some improvements for replication.md

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* Mention clickhouse-backup tool

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2018-12-12 20:28:00 +03:00

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# External Data for Query Processing
ClickHouse allows sending a server the data that is needed for processing a query, together with a SELECT query. This data is put in a temporary table (see the section "Temporary tables") and can be used in the query (for example, in IN operators).
For example, if you have a text file with important user identifiers, you can upload it to the server along with a query that uses filtration by this list.
If you need to run more than one query with a large volume of external data, don't use this feature. It is better to upload the data to the DB ahead of time.
External data can be uploaded using the command-line client (in non-interactive mode), or using the HTTP interface.
In the command-line client, you can specify a parameters section in the format
```bash
--external --file=... [--name=...] [--format=...] [--types=...|--structure=...]
```
You may have multiple sections like this, for the number of tables being transmitted.
**--external** Marks the beginning of a clause.
**--file** Path to the file with the table dump, or -, which refers to stdin.
Only a single table can be retrieved from stdin.
The following parameters are optional: **--name** Name of the table. If omitted, _data is used.
**--format** Data format in the file. If omitted, TabSeparated is used.
One of the following parameters is required:**--types** A list of comma-separated column types. For example: `UInt64,String`. The columns will be named _1, _2, ...
**--structure** The table structure in the format`UserID UInt64`, `URL String`. Defines the column names and types.
The files specified in 'file' will be parsed by the format specified in 'format', using the data types specified in 'types' or 'structure'. The table will be uploaded to the server and accessible there as a temporary table with the name in 'name'.
Examples:
```bash
echo -ne "1\n2\n3\n" | clickhouse-client --query="SELECT count() FROM test.visits WHERE TraficSourceID IN _data" --external --file=- --types=Int8
849897
cat /etc/passwd | sed 's/:/\t/g' | clickhouse-client --query="SELECT shell, count() AS c FROM passwd GROUP BY shell ORDER BY c DESC" --external --file=- --name=passwd --structure='login String, unused String, uid UInt16, gid UInt16, comment String, home String, shell String'
/bin/sh 20
/bin/false 5
/bin/bash 4
/usr/sbin/nologin 1
/bin/sync 1
```
When using the HTTP interface, external data is passed in the multipart/form-data format. Each table is transmitted as a separate file. The table name is taken from the file name. The 'query_string' is passed the parameters 'name_format', 'name_types', and 'name_structure', where 'name' is the name of the table that these parameters correspond to. The meaning of the parameters is the same as when using the command-line client.
Example:
```bash
cat /etc/passwd | sed 's/:/\t/g' > passwd.tsv
curl -F 'passwd=@passwd.tsv;' 'http://localhost:8123/?query=SELECT+shell,+count()+AS+c+FROM+passwd+GROUP+BY+shell+ORDER+BY+c+DESC&passwd_structure=login+String,+unused+String,+uid+UInt16,+gid+UInt16,+comment+String,+home+String,+shell+String'
/bin/sh 20
/bin/false 5
/bin/bash 4
/usr/sbin/nologin 1
/bin/sync 1
```
For distributed query processing, the temporary tables are sent to all the remote servers.
[Original article](https://clickhouse.yandex/docs/en/operations/table_engines/external_data/) <!--hide-->