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57 lines
3.3 KiB
ReStructuredText
57 lines
3.3 KiB
ReStructuredText
External data for query processing
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====================================
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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).
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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.
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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.
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External data can be uploaded using the command-line client (in non-interactive mode), or using the HTTP interface.
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In the command-line client, you can specify a parameters section in the format
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::
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--external --file=... [--name=...] [--format=...] [--types=...|--structure=...]
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You may have multiple sections like this, for the number of tables being transmitted.
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**--external** - Marks the beginning of the section.
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**--file** - Path to the file with the table dump, or ``-``, which refers to stdin
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Only a single table can be retrieved from stdin.
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The following parameters are optional:
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**--name** - Name of the table. If omitted, ``_data`` is used.
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**--format** - Data format in the file. If omitted, ``TabSeparated`` is used.
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One of the following parameters is required:
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**--types** - A comma-separated list of column types. For example, ``UInt64,String``. Columns will be named ``_1``, ``_2``, ...
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**--structure** - Table structure, in the format ``UserID UInt64, URL String``. Defines the column names and types.
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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 ``name``.
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Examples:
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::
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echo -ne "1\n2\n3\n" | clickhouse-client --query="SELECT count() FROM test.visits WHERE TraficSourceID IN _data" --external --file=- --types=Int8
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849897
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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'
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/bin/sh 20
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/bin/false 5
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/bin/bash 4
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/usr/sbin/nologin 1
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/bin/sync 1
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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' passes 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.
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Example:
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::
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cat /etc/passwd | sed 's/:/\t/g' > passwd.tsv
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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'
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/bin/sh 20
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/bin/false 5
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/bin/bash 4
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/usr/sbin/nologin 1
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/bin/sync 1
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For distributed query processing, the temporary tables are sent to all the remote servers.
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