feature: External Table ( for ClickHouse )

[zliang-min]

PR checklist:

• Did you run ClangFormat ?
• Did you separate headers to a different section in existing community code base ?
• Did you surround proton: starts/ends for new code in existing community code base ?

Please write user-readable short description of the changes:

New feature for creating External Tabels to connect to non-streaming data sources. In this first implementation, a ClickHouse External Table has been implemented.

Examples:

To create an external table:

CREATE EXTERNAL TABLE my_first_table SETTINGS type='clickhouse',address='my_clickhouse_server:9000',database='my_database',table='my_table',user='my_user',passowrd='my_password'

External tables do not accept the column list, it fetches its table structure from the remote data source. After the table is created, one can use DESCRIBE my_table to see its structure.

Then, it can be queried just like any tables/streams:

-- read data
SELECT * FROM my_external_table;

-- write data
INSERT INTO my_external_table VALUES (...);

-- use it as a materialized view target
CREATE MATERIALIZED VIEW some_view INTO my_external_table AS SELECT ...;

To drop an external table:

DROP EXTERNAL TABLE my_table

[jovezhong]

Hi @zliang-min , please test the behavior of connecting to a view or materialized view in ClickHouse.

Probably Proton can still read it but cannot write to it. If the user creates an external table connecting to a ClickHouse view, then try to use it as target for Proton Materialized view. The materialized view DDL should fail, instead of creation is done but no result while MV is running

[zliang-min]

Hi @zliang-min , please test the behavior of connecting to a view or materialized view in ClickHouse.

Probably Proton can still read it but cannot write to it. If the user creates an external table connecting to a ClickHouse view, then try to use it as target for Proton Materialized view. The materialized view DDL should fail, instead of creation is done but no result while MV is running

Checked, it works for views and materialized views (read-only of course).

[jovezhong]

(Jove Github Bot) added it to the current sprint.

[jovezhong]

(Jove Github Bot) moved this ticket out of the GitHub project(up to 1200 tickets for one project).