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ClickHouse provides two types of client APIs over HTTP and TCP protocols respectively.

Over HTTP

HTTP is mainly used to support simple lightweight operations and suitable in cross-platform and cross-programming language scenarios. The clickhouse-server process on the EMR cluster can start the HTTP service at port 8123 to send simple GET requests in order to check whether the service is normal.

$ curl http://127.0.0.1:8123
Ok.

You can also send requests through query parameters. For example, the following sample code is to query data in the account table in testdb:

$ wget -q -O- 'http://127.0.0.1:8123/?query=SELECT * from testdb.account'
1       GHua    WuHan Hubei     1990
2       SLiu    ShenZhen Guangzhou      1991
3       JPong   Chengdu Sichuan 1992

For other methods, please see HTTP Interface.

Over TCP

TCP is used mainly on clickhouse-client. You can enter the clickhouse-client command in the EMR cluster to get information such as the version information, address of the connected clickhouse-server, and database used by default. You can run quit, exit, or q to exit.

$ clickhouse-client
ClickHouse client version 19.16.12.49.
Connecting to localhost:9000 as user default.
Connected to ClickHouse server version 19.16.12 revision 54427.

Key parameters used by clickhouse-client:

• -C --config-file: configuration file used by client.
• -h --host: IP address of clickhouse-server.
• --port: port address of clickhouse-server.
• -u --user: username.
• --password: password.
• -d --database: database name.
• -V --version: displays client version.
• -E --vertical: displays query results in vertical format.
• -q --query: passed-in SQL statement in non-interactive mode.
• -t --time: displays execution time in non-interactive mode.
• --log-level: client log level.
• --send_logs_level: level of log data returned by server.
• --server_logs_file: server log storage path.

For other parameters, please see Command-line Client.