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* Some improvements for introduction/performance.md
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78 lines
1.8 KiB
Markdown
78 lines
1.8 KiB
Markdown
<a name="table_engines-url"></a>
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# URL(URL, Format)
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This data source operates with data on remote HTTP/HTTPS server. The engine is
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similar to [`File`](./file.md#).
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## Usage in ClickHouse Server
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```
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URL(URL, Format)
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```
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`Format` should be supported for `SELECT` and/or `INSERT`. For the full list of
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supported formats see [Formats](../../interfaces/formats.md#formats).
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`URL` must match the format of Uniform Resource Locator. The specified
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URL must address a server working with HTTP or HTTPS. The server shouldn't
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require any additional HTTP-headers.
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`INSERT` and `SELECT` queries are transformed into `POST` and `GET` requests
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respectively. For correct `POST`-requests handling the remote server should support
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[Chunked transfer encoding](https://ru.wikipedia.org/wiki/Chunked_transfer_encoding).
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**Example:**
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**1.** Create the `url_engine_table` table:
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```sql
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CREATE TABLE url_engine_table (word String, value UInt64)
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ENGINE=URL('http://127.0.0.1:12345/', CSV)
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```
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**2.** Implement simple http-server using python3:
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```python3
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from http.server import BaseHTTPRequestHandler, HTTPServer
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class CSVHTTPServer(BaseHTTPRequestHandler):
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def do_GET(self):
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self.send_response(200)
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self.send_header('Content-type', 'text/csv')
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self.end_headers()
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self.wfile.write(bytes('Hello,1\nWorld,2\n', "utf-8"))
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if __name__ == "__main__":
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server_address = ('127.0.0.1', 12345)
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HTTPServer(server_address, CSVHTTPServer).serve_forever()
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```
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```bash
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python3 server.py
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```
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**3.** Query the data:
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```sql
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SELECT * FROM url_engine_table
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```
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```text
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┌─word──┬─value─┐
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│ Hello │ 1 │
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│ World │ 2 │
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└───────┴───────┘
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```
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## Details of Implementation
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- Reads and writes can be parallel
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- Not supported:
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- `ALTER`
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- `SELECT ... SAMPLE`
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- Indices
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- Replication
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