feat(parser): ClickHouse parametric aggregates (#482) (#487)

* feat(parser): ClickHouse parametric aggregates fn(p)(args) (#482)

* fix(ast): include Parameters in FunctionCall.Children() (#482 review)

---------

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

Author: ajitpratap0

pkg/sql/ast/ast.go

@@ -692,6 +692,7 @@ func (i Identifier) Children() []Node     { return nil }
 type FunctionCall struct {
 	Name          string
 	Arguments     []Expression // Renamed from Args for consistency
+	Parameters    []Expression // ClickHouse parametric aggregates: quantile(0.5)(x) — params before args
 	Over          *WindowSpec  // For window functions
 	Distinct      bool
 	Filter        Expression          // WHERE clause for aggregate functions
@@ -705,6 +706,9 @@ func (f *FunctionCall) expressionNode()     {}
 func (f FunctionCall) TokenLiteral() string { return f.Name }
 func (f FunctionCall) Children() []Node {
 	children := nodifyExpressions(f.Arguments)
+	if len(f.Parameters) > 0 {
+		children = append(children, nodifyExpressions(f.Parameters)...)
+	}
 	if f.Over != nil {
 		children = append(children, f.Over)
 	}

pkg/sql/parser/clickhouse_parametric_test.go

@@ -0,0 +1,74 @@
+// 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/ast"
+	"github.com/ajitpratap0/GoSQLX/pkg/sql/keywords"
+)
+
+// TestClickHouseParametricAggregates verifies that ClickHouse parametric
+// aggregates of the form `funcName(params)(args)` parse. Regression for #482.
+func TestClickHouseParametricAggregates(t *testing.T) {
+	queries := map[string]string{
+		"quantile_tdigest": `SELECT quantileTDigest(0.95)(value) FROM events`,
+		"top_k":            `SELECT topK(10)(name) FROM users`,
+		"quantiles":        `SELECT quantiles(0.5, 0.9, 0.99)(latency_ms) FROM requests`,
+		"with_group_by":    `SELECT category, quantileTDigest(0.99)(price) FROM products GROUP BY category`,
+	}
+	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)
+			}
+		})
+	}
+}
+
+// TestClickHouseParametricAggregates_ASTShape verifies that the Parameters
+// field is populated and reachable via the visitor pattern.
+func TestClickHouseParametricAggregates_ASTShape(t *testing.T) {
+	q := `SELECT quantileTDigest(0.95)(value) FROM events`
+	tree, err := gosqlx.ParseWithDialect(q, keywords.DialectClickHouse)
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	// Walk the tree until we find a FunctionCall node and verify both
+	// Parameters and Arguments are populated, and Children() exposes both.
+	var found bool
+	var visit func(n ast.Node)
+	visit = func(n ast.Node) {
+		if n == nil || found {
+			return
+		}
+		if fc, ok := n.(*ast.FunctionCall); ok && fc.Name == "quantileTDigest" {
+			if len(fc.Parameters) != 1 {
+				t.Fatalf("Parameters: want 1, got %d", len(fc.Parameters))
+			}
+			if len(fc.Arguments) != 1 {
+				t.Fatalf("Arguments: want 1, got %d", len(fc.Arguments))
+			}
+			// Children() must include both the argument and the parameter.
+			if len(fc.Children()) < 2 {
+				t.Fatalf("Children(): want >=2 (args + params), got %d", len(fc.Children()))
+			}
+			found = true
+			return
+		}
+		for _, c := range n.Children() {
+			visit(c)
+		}
+	}
+	for _, stmt := range tree.Statements {
+		visit(stmt)
+	}
+	if !found {
+		t.Fatal("did not find quantileTDigest FunctionCall in AST")
+	}
+}

pkg/sql/parser/window.go

@@ -23,6 +23,7 @@ import (
 
 	"github.com/ajitpratap0/GoSQLX/pkg/models"
 	"github.com/ajitpratap0/GoSQLX/pkg/sql/ast"
+	"github.com/ajitpratap0/GoSQLX/pkg/sql/keywords"
 )
 
 // SUM(salary) OVER (PARTITION BY dept ORDER BY date ROWS UNBOUNDED PRECEDING) -> window function with frame
@@ -153,6 +154,36 @@ func (p *Parser) parseFunctionCall(funcName string) (*ast.FunctionCall, error) {
 		OrderBy:   orderByExprs,
 	}
 
+	// ClickHouse parametric aggregates: funcName(params)(args).
+	// e.g. quantileTDigest(0.95)(value), topK(10)(name).
+	// What we just parsed becomes Parameters; the next paren group is the
+	// real arguments. Gated to ClickHouse to avoid false positives.
+	if p.dialect == string(keywords.DialectClickHouse) && p.isType(models.TokenTypeLParen) {
+		funcCall.Parameters = funcCall.Arguments
+		funcCall.Arguments = nil
+		p.advance() // Consume second (
+		if !p.isType(models.TokenTypeRParen) {
+			for {
+				arg, err := p.parseExpression()
+				if err != nil {
+					return nil, err
+				}
+				funcCall.Arguments = append(funcCall.Arguments, arg)
+				if p.isType(models.TokenTypeComma) {
+					p.advance()
+				} else if p.isType(models.TokenTypeRParen) {
+					break
+				} else {
+					return nil, p.expectedError(", or )")
+				}
+			}
+		}
+		if !p.isType(models.TokenTypeRParen) {
+			return nil, p.expectedError(")")
+		}
+		p.advance() // Consume second )
+	}
+
 	// Check for IGNORE NULLS / RESPECT NULLS (SQL:2016 null treatment).
 	// Used by LAG, LEAD, FIRST_VALUE, LAST_VALUE, NTH_VALUE in Snowflake,
 	// Oracle, BigQuery, etc. IGNORE arrives as TokenTypeKeyword; RESPECT is