feat(parser): ClickHouse ORDER BY ... WITH FILL (#482) (#493)

Co-authored-by: Ajit Pratap Singh <ajitpratapsingh@Ajits-Mac-mini-2655.local>

Author: ajitpratap0

pkg/sql/parser/clickhouse_with_fill_test.go

@@ -0,0 +1,34 @@
+// Copyright 2026 GoSQLX Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+
+package parser_test
+
+import (
+	"testing"
+
+	"github.com/ajitpratap0/GoSQLX/pkg/gosqlx"
+	"github.com/ajitpratap0/GoSQLX/pkg/sql/keywords"
+)
+
+// TestClickHouseOrderByWithFill verifies ClickHouse's `ORDER BY expr WITH
+// FILL [FROM..] [TO..] [STEP..]` modifier parses. Previously the WITH token
+// after ORDER BY items was mis-routed to the WITH-CTE parser. Regression
+// for #482.
+func TestClickHouseOrderByWithFill(t *testing.T) {
+	queries := map[string]string{
+		"bare":          `SELECT id FROM t ORDER BY id WITH FILL`,
+		"step_only":     `SELECT id FROM t ORDER BY id WITH FILL STEP 1`,
+		"from_to_step":  `SELECT day, count() FROM events GROUP BY day ORDER BY day WITH FILL FROM '2024-01-01' TO '2024-12-31' STEP INTERVAL 1 DAY`,
+		"multiple_cols": `SELECT a, b FROM t ORDER BY a WITH FILL STEP 1, b`,
+		"with_desc":     `SELECT id FROM t ORDER BY id DESC WITH FILL STEP 1`,
+	}
+	for name, q := range queries {
+		q := q
+		t.Run(name, func(t *testing.T) {
+			if _, err := gosqlx.ParseWithDialect(q, keywords.DialectClickHouse); err != nil {
+				t.Fatalf("parse failed: %v", err)
+			}
+		})
+	}
+}

pkg/sql/parser/select_clauses.go

@@ -548,6 +548,17 @@ func (p *Parser) parseOrderByClause() ([]ast.OrderByExpression, error) {
 		}
 		entry.NullsFirst = nullsFirst
 
+		// ClickHouse WITH FILL per-entry tail:
+		//   ORDER BY expr [ASC|DESC] WITH FILL [FROM x] [TO y] [STEP z]
+		// Consume permissively; the clause is not modeled on the AST yet.
+		if p.dialect == string(keywords.DialectClickHouse) &&
+			p.isType(models.TokenTypeWith) &&
+			strings.EqualFold(p.peekToken().Token.Value, "FILL") {
+			p.advance() // WITH
+			p.advance() // FILL
+			p.skipClickHouseWithFillTail()
+		}
+
 		orderByExprs = append(orderByExprs, entry)
 
 		if !p.isType(models.TokenTypeComma) {
@@ -558,6 +569,26 @@ func (p *Parser) parseOrderByClause() ([]ast.OrderByExpression, error) {
 	return orderByExprs, nil
 }
 
+// skipClickHouseWithFillTail consumes the optional FROM / TO / STEP arguments
+// of a ClickHouse "ORDER BY expr WITH FILL" modifier. Each argument is a
+// single expression (possibly an INTERVAL). The tail ends at the next comma
+// (more ORDER BY items), next clause keyword, ';', or EOF.
+func (p *Parser) skipClickHouseWithFillTail() {
+	for {
+		val := strings.ToUpper(p.currentToken.Token.Value)
+		if val != "FROM" && val != "TO" && val != "STEP" {
+			return
+		}
+		p.advance() // FROM / TO / STEP
+		// Consume one expression; ignore parse errors so unusual forms
+		// (INTERVAL '1 day', expressions with function calls, etc.) don't
+		// surface as parser errors for this permissive skip.
+		if _, err := p.parseExpression(); err != nil {
+			return
+		}
+	}
+}
+
 // parseLimitOffsetClause parses optional LIMIT and/or OFFSET clauses.
 // Supports standard "LIMIT n OFFSET m", MySQL "LIMIT offset, count", and
 // SQL-99 "OFFSET n ROWS" (ROW/ROWS consumed but value stored).