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107 lines
4.5 KiB
Markdown
107 lines
4.5 KiB
Markdown
---
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slug: /en/engines/table-functions/executable
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sidebar_position: 50
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sidebar_label: executable
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keywords: [udf, user defined function, clickhouse, executable, table, function]
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---
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# executable Table Function for UDFs
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The `executable` table function creates a table based on the output of a user-defined function (UDF) that you define in a script that outputs rows to **stdout**. The executable script is stored in the `users_scripts` directory and can read data from any source.
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You can optionally include one or more input queries that stream their results to **stdin** for the script to read.
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:::note
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A key advantage between ordinary UDF functions and the `executable` table function and `Executable` table engine is that ordinary UDF functions cannot change the row count. For example, if the input is 100 rows, then the result must return 100 rows. When using the `executable` table function or `Executable` table engine, your script can make any data transformations you want, including complex aggregations.
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:::
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## Syntax
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The `executable` table function requires three parameters and accepts an optional list of input queries:
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```sql
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executable(script_name, format, structure, [input_query...] [,SETTINGS ...])
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```
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- `script_name`: the file name of the script. saved in the `user_scripts` folder (the default folder of the `user_scripts_path` setting)
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- `format`: the format of the generated table
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- `structure`: the table schema of the generated table
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- `input_query`: an optional query (or collection or queries) whose results are passed to the script via **stdin**
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:::note
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If you are going to invoke the same script repeatedly with the same input queries, consider using the [`Executable` table engine](../../engines/table-engines/special/executable.md).
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:::
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The following Python script is named `generate_random.py` and is saved in the `user_scripts` folder. It reads in a number `i` and prints `i` random strings, with each string preceded by a number that is separated by a tab:
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```python
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#!/usr/local/bin/python3.9
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import sys
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import string
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import random
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def main():
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# Read input value
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for number in sys.stdin:
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i = int(number)
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# Generate some random rows
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for id in range(0, i):
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letters = string.ascii_letters
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random_string = ''.join(random.choices(letters ,k=10))
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print(str(id) + '\t' + random_string + '\n', end='')
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# Flush results to stdout
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sys.stdout.flush()
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if __name__ == "__main__":
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main()
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```
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Let's invoke the script and have it generate 10 random strings:
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```sql
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SELECT * FROM executable('my_script.py', TabSeparated, 'id UInt32, random String', (SELECT 10))
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```
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The response looks like:
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```response
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┌─id─┬─random─────┐
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│ 0 │ xheXXCiSkH │
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│ 1 │ AqxvHAoTrl │
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│ 2 │ JYvPCEbIkY │
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│ 3 │ sWgnqJwGRm │
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│ 4 │ fTZGrjcLon │
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│ 5 │ ZQINGktPnd │
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│ 6 │ YFSvGGoezb │
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│ 7 │ QyMJJZOOia │
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│ 8 │ NfiyDDhmcI │
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│ 9 │ REJRdJpWrg │
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└────┴────────────┘
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```
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## Settings
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- `send_chunk_header` - controls whether to send row count before sending a chunk of data to process. Default value is `false`.
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- `pool_size` — Size of pool. If 0 is specified as `pool_size` then there is no pool size restrictions. Default value is `16`.
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- `max_command_execution_time` — Maximum executable script command execution time for processing block of data. Specified in seconds. Default value is 10.
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- `command_termination_timeout` — executable script should contain main read-write loop. After table function is destroyed, pipe is closed, and executable file will have `command_termination_timeout` seconds to shutdown, before ClickHouse will send SIGTERM signal to child process. Specified in seconds. Default value is 10.
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- `command_read_timeout` - timeout for reading data from command stdout in milliseconds. Default value 10000.
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- `command_write_timeout` - timeout for writing data to command stdin in milliseconds. Default value 10000.
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## Passing Query Results to a Script
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Be sure to check out the example in the `Executable` table engine on [how to pass query results to a script](../../engines/table-engines/special/executable.md#passing-query-results-to-a-script). Here is how you execute the same script in that example using the `executable` table function:
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```sql
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SELECT * FROM executable(
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'sentiment.py',
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TabSeparated,
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'id UInt64, sentiment Float32',
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(SELECT id, comment FROM hackernews WHERE id > 0 AND comment != '' LIMIT 20)
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);
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```
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