Add SQL grammar documentation for PenguinDB

[rahulc0dy]

Issue Reference

• Fixes part of Define AST Nodes & SQL Grammar #11

Summary by CodeRabbit

• Documentation
  • Added a comprehensive PenguinDB SQL grammar (BNF + readable EBNF) covering full statement syntax for DDL/DML, expression/operator precedence, function/call and join forms, data types, lexical rules and case-sensitivity, literals and string-escaping, WHERE boolean logic with precedence/grouping, and notes on constraint ordering and special-case behaviors.

[coderabbitai]

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Walkthrough

Adds docs/grammar.md, a complete PenguinDB SQL grammar in BNF and EBNF, including lexical rules, DDL for databases/tables, DML statements, expression precedence, data types, token definitions, and reference notes.

Changes

SQL Grammar Documentation

Layer / File(s)	Summary
Document header and lexical rules docs/grammar.md	Document header and global lexical rule: keywords and unquoted identifiers are case-insensitive; single-quoted strings preserve casing.
BNF grammar (statements, DDL, DML, expressions) docs/grammar.md	Full BNF covering program/statement structure; CREATE/ALTER/DROP DATABASE/TABLE; column constraints and ordering; SELECT/INSERT/UPDATE/DELETE; WHERE boolean precedence; expression/operator precedence.
EBNF restatement docs/grammar.md	Readable EBNF restatement of the same grammar covering statements, clauses, expressions, data types, identifiers, and literals.
Reference notes docs/grammar.md	Notes summarizing semicolon-terminated scripts, identifier/literal character rules, numeric/string literal specifics (including '' escaping), select-expression ambiguity guidance, and canonical constraint ordering.

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[coderabbitai]

Actionable comments posted: 2

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: cef01870-a83e-48d8-9045-11b15094c49a

📥 Commits

Reviewing files that changed from the base of the PR and between 9601155 and ed20d93.

📒 Files selected for processing (3)

• docs/grammar.md
• docs/sql-grammar/grammar.bnf
• docs/sql-grammar/grammar.ebnf

[Souvik606]

Please check and resolve these changes

[Souvik606]

Please fix these sql specific patterns

[rahulc0dy]

Following additional rules are to be implemented:

1. Strings to accept all non single quote characters
2. Add IF EXISTS / IF NOT EXISTS
3. Add ORDER BY clause
4. Add LIKE predicate
5. Add IS NULL / IS NOT NULL predicate
6. Add IN predicate
7. Add BETWEEN predicate
8. NullConstraint → support both NULL and NOT NULL
9. Add unary + support
10. Add DISTINCT in SELECT
11. GROUP BY / HAVING
12. Add aggregate functions
13. Add JOIN syntax
14. Add qualified column references (table.column)
15. Add OFFSET