ClickHouse/docs/en/engines/table_engines/special/url.md
2020-04-08 17:22:25 +03:00

81 lines
2.3 KiB
Markdown

---
toc_priority: 41
toc_title: URL
---
# URL(URL, Format) {#table_engines-url}
Manages data on a remote HTTP/HTTPS server. This engine is similar
to the [File](file.md) engine.
## Using the Engine In the ClickHouse Server {#using-the-engine-in-the-clickhouse-server}
The `format` must be one that ClickHouse can use in
`SELECT` queries and, if necessary, in `INSERTs`. For the full list of supported formats, see
[Formats](../../../interfaces/formats.md#formats).
The `URL` must conform to the structure of a Uniform Resource Locator. The specified URL must point to a server
that uses HTTP or HTTPS. This does not require any
additional headers for getting a response from the server.
`INSERT` and `SELECT` queries are transformed to `POST` and `GET` requests,
respectively. For processing `POST` requests, the remote server must support
[Chunked transfer encoding](https://en.wikipedia.org/wiki/Chunked_transfer_encoding).
You can limit the maximum number of HTTP GET redirect hops using the [max\_http\_get\_redirects](../../../operations/settings/settings.md#setting-max_http_get_redirects) setting.
**Example:**
**1.** Create a `url_engine_table` table on the server :
``` sql
CREATE TABLE url_engine_table (word String, value UInt64)
ENGINE=URL('http://127.0.0.1:12345/', CSV)
```
**2.** Create a basic HTTP server using the standard Python 3 tools and
start it:
``` python3
from http.server import BaseHTTPRequestHandler, HTTPServer
class CSVHTTPServer(BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(200)
self.send_header('Content-type', 'text/csv')
self.end_headers()
self.wfile.write(bytes('Hello,1\nWorld,2\n', "utf-8"))
if __name__ == "__main__":
server_address = ('127.0.0.1', 12345)
HTTPServer(server_address, CSVHTTPServer).serve_forever()
```
``` bash
$ python3 server.py
```
**3.** Request data:
``` sql
SELECT * FROM url_engine_table
```
``` text
┌─word──┬─value─┐
│ Hello │ 1 │
│ World │ 2 │
└───────┴───────┘
```
## Details Of Implementation {#details-of-implementation}
- Reads and writes can be parallel
- Not supported:
- `ALTER` and `SELECT...SAMPLE` operations.
- Indexes.
- Replication.
[Original article](https://clickhouse.tech/docs/en/operations/table_engines/url/) <!--hide-->