docs: missing documentation for NUMBERS, NUMBERS_MT, and NUMBERS_LOCAL table functions

Start with the registrations in src/query/service/src/table_functions/table_function_factory.rs and the existing docs/en/sql-reference/00-sql-reference/31-system-tables/system-numbers.md page. Add docs/en/sql-reference/20-sql-functions/17-table-functions/numbers.md covering numbers, numbers_mt, and numbers_local, including syntax, arguments, return schema, parallelism, and examples. Done means all three functions have a dedicated SQL reference page.

Summary

The numbers, numbers_mt, and numbers_local table functions are registered in the table function factory but are only documented as a system table (system.numbers), not as table functions in the SQL reference table-functions section.

Source

• File: /workspace/databend/src/query/service/src/table_functions/table_function_factory.rs
• Registration (lines 128–142): All three variants are registered via NumbersTable::create

creators.insert("numbers".to_string(), (next_id(), number_table_func_creator.clone()));
creators.insert("numbers_mt".to_string(), (next_id(), number_table_func_creator.clone()));
creators.insert("numbers_local".to_string(), (next_id(), number_table_func_creator));

What They Do

These table functions generate a sequence of integers starting from 0:

• numbers(N) — Generates N rows with a single UInt64 column number (0 to N-1). Parallelized across all available threads.
• numbers_mt(N) — Same as numbers, explicitly multi-threaded.
• numbers_local(N) — Same but runs on a single thread (local execution).

They are widely used for testing, benchmarking, and generating synthetic datasets. Example:

SELECT avg(number) FROM numbers(100000000);
SELECT sum(number) FROM numbers_mt(1000000) WHERE number % 2 = 0;

What's Missing

The existing system.numbers page at /docs/en/sql-reference/00-sql-reference/31-system-tables/system-numbers.md only briefly mentions the function call syntax. There is no dedicated table-function reference page covering all three variants, their differences (parallelism behavior), and usage patterns.

The SHOW TABLE FUNCTIONS output lists numbers, numbers_mt, and numbers_local but users have no reference page to link to.

Suggested Doc Location

/docs/en/sql-reference/20-sql-functions/17-table-functions/numbers.md

The page should cover all three variants, explain the parallelism difference, include the syntax, argument description, return schema, and examples.