Multiple join emulation (very experimental - developers only)

[4ertus2]

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Category (leave one):

• New Feature

Short description (up to few sentences):
multiple joins emulation (very experimental)

Detailed description (optional):
Allow some queries with multiple INNER JOINs.

[sartor]

First of all, thank you for your work!
I've already check this feature and it is working!
But:

1. Are you planning to allow multiple left joins?
2. There is problem now with aliases: If all table has alias - we must use prefix for column that are ambiguous in query and we do not allow to use column name with alias prefix for unique names.
   Example:

CREATE TABLE dispatches
(
  id                Int64,
  rule_id           Int32,
  segment_id        Int32
);

CREATE TABLE rules
(
  id            Int32,
  title         String
);

CREATE TABLE segments
(
  id            Int32,
  name         String
);

I must write query (working now):

SELECT 
    name, 
    COUNT(*)
FROM dispatches AS d 
ALL INNER JOIN segments AS s ON s.id = segment_id
ALL INNER JOIN rules AS r ON r.id = rule_id
GROUP BY name

But I want to specify table aliases for all columns (not working now):

SELECT 
    s.name, 
    COUNT(*)
FROM dispatches AS d 
ALL INNER JOIN segments AS s ON s.id = d.segment_id
ALL INNER JOIN rules AS r ON r.id = d.rule_id
GROUP BY s.name