[Refactor] Add basic formatter

[colinthebomb1]

Overview:

This PR implements a basic formatter with a basic test for converting from our custom AST into JSON that can be understood by mosql, which turns it into plaintext. AST -> JSON -> SQL TEXT (via mosql).

Code Changes:

• In tests/test_query_parser.py added test_basic_format() to run a basic test of the formatter and normalize_sql() for comparing if the expected sql is equal to our output.
• Implemented format() and it's clause specific formatters: format_select(), format_from() ...etc in core/query_parser.py, responsible for converting AST to JSON clause by clause.

[colinthebomb1]

@HazelYuAhiru Because the test case assumes your output will match its input, I want to make sure our AST matches. The changes I made are:

• Implemented order by using new OrderByItem node

order_by_clause = OrderByNode([
        OrderByItemNode(dept_alias, SortOrder.DESC),
        OrderByItemNode(count_alias, SortOrder.DESC)  
])  

• Changed all sets to lists
• added dept alias for order by dept_alias = ColumnNode("dept_name")
• added alias to count star FunctionNode count_star = FunctionNode("COUNT", {ColumnNode("*")}, 'emp_count')

[HazelYuAhiru]

I'm still reviewing the main formatter functions, but I was wondering that should we separate the formatter and parser code into different files with their own tests? Like having query_formatter.py and query_formatter_test.py to avoid future merge conflicts.

[HazelYuAhiru]

LGTM!

[Copilot]

Pull request overview

This PR implements a basic query formatter that converts custom AST (Abstract Syntax Tree) nodes into JSON format compatible with the mosql library, which then generates SQL text. The implementation provides a two-step conversion pipeline: AST → JSON → SQL.

Key Changes:

• Added QueryFormatter class with format() method that orchestrates the AST-to-SQL conversion
• Implemented clause-specific formatters (format_select, format_from, format_where, etc.) to handle different SQL clauses
• Created comprehensive test case test_basic_format() that validates formatting of a complex query with JOIN, WHERE, GROUP BY, HAVING, ORDER BY, LIMIT, and OFFSET clauses

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 11 comments.

File	Description
core/query_formatter.py	New formatter implementation with AST-to-JSON conversion functions and support for all major SQL clauses including JOIN operations
tests/test_query_formatter.py	New test file with test_basic_format() validating the formatter against a comprehensive multi-clause SQL query, plus normalize_sql() helper for SQL comparison

Comments suppressed due to low confidence (3)

core/query_formatter.py:8

• Import of 'ColumnNode' is not used.
  Import of 'LiteralNode' is not used.
  Import of 'OperatorNode' is not used.
  Import of 'FunctionNode' is not used.
  Import of 'LimitNode' is not used.
  Import of 'OffsetNode' is not used.
  Import of 'SubqueryNode' is not used.
  Import of 'VarNode' is not used.
  Import of 'VarSetNode' is not used.

from core.ast.node import (
    QueryNode, SelectNode, FromNode, WhereNode, TableNode, ColumnNode, 
    LiteralNode, OperatorNode, FunctionNode, GroupByNode, HavingNode,
    OrderByNode, LimitNode, OffsetNode, SubqueryNode, VarNode, VarSetNode,
    JoinNode
)

tests/test_query_formatter.py:7

• Import of 'SubqueryNode' is not used.
  Import of 'VarNode' is not used.
  Import of 'VarSetNode' is not used.

from core.ast.node import (
    OrderByItemNode, QueryNode, SelectNode, FromNode, WhereNode, TableNode, ColumnNode, 
    LiteralNode, OperatorNode, FunctionNode, GroupByNode, HavingNode,
    OrderByNode, LimitNode, OffsetNode, SubqueryNode, VarNode, VarSetNode, JoinNode
)

tests/test_query_formatter.py:9

• Import of 'get_query' is not used.

from data.queries import get_query

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[baiqiushi]

Thanks @colinthebomb1 for the PR! It looks great overall! Only a few minor changes are needed. Please take care of them. Thanks!