Optimize join tables from different databases: executor

[ea-rus]

Description

Updates:

Subselect step is used to get value from previous step data.

select distinct <column> from <step data1>

Next step is fetching data using these values as filter

select * from db2.table2 where <column> in (<ids from previous step>)

Side fix:
If join is without condition:

• add 0=0 filter (multiply rows)
• but use limitation. If expected number of rows is exceed limit - raise exception

Dependent on mindsdb/mindsdb_sql#412

Fixes #issue_number

Type of change

• ⚡ New feature (non-breaking change which adds functionality)

Verification Process

To ensure the changes are working as expected:

• Test Location: Specify the URL or path for testing.
• Verification Steps: Outline the steps or queries needed to validate the change. Include any data, configurations, or actions required to reproduce or see the new functionality.

Additional Media:

• I have attached a brief loom video or screenshots showcasing the new functionality or change.

Checklist:

• [x My code follows the style guidelines(PEP 8) of MindsDB.
• I have appropriately commented on my code, especially in complex areas.
• Necessary documentation updates are either made or tracked in issues.
• Relevant unit and integration tests are updated or added.

[StpMax]

Are left_data and right_data dataframes? If so, then may be better to get real size (df.memory_usage(index=True, deep=True).sum()) and compare with free memory?

[ea-rus]

They are ResultSets