[PATCH] Add support for INSERT ... SET syntax

Hi,

I would like to propose adding support for an alternative INSERT syntax
that uses named column assignments via a SET clause. This provides a more
convenient and readable way to write inserts, particularly when only
specific columns need values.

Currently, PostgreSQL requires INSERT statements to separate the column
list from the values:

INSERT INTO users (name, email, status) VALUES ('Alice', '
alice(at)example(dot)com', 'active');

For inserts with many columns or where only a subset of columns are
specified, the proposed SET syntax offers better readability by keeping
column names adjacent to their values:

INSERT INTO users SET name='Alice', email='alice(at)example(dot)com',
status='active';

Proposed Syntax:

INSERT INTO table_name
SET (column1=value1, column2=value2, ...), (, ...)
[ ON CONFLICT ... ]
[ RETURNING ... ];

Below INSERT features are supported:
- DEFAULT keyword: SET col=DEFAULT
- Expressions and functions: SET col=expr, col2=function(...)
- Subqueries: SET col=(SELECT ...)
- RETURNING clause
- ON CONFLICT DO UPDATE/NOTHING
- OVERRIDING SYSTEM VALUE
- Multi-row syntax: SET (col1=val1, col2=val2), (col1=val3, col2=val4)

Columns not mentioned receive their default values or NULL, consistent with
standard INSERT behavior.

I've attached the patch. Looking forward to your feedback.
--

Thanks & Regards,
Suraj kharage,

enterprisedb.com <https://www.enterprisedb.com/>