fix(parser): allow TABLE/PARTITION/TABLES as identifiers in ClickHouse (#480)

ClickHouse system tables (system.replicas, system.parts, system.tables) expose
columns named `table` and `partition`, and queries commonly reference
`system.tables`. The parser previously rejected these because TABLE, PARTITION,
and TABLES tokenize as keywords and the non-reserved-keyword-as-identifier path
was gated to SQL Server only.

- Extend the gate in parsePrimaryExpression to also enable for ClickHouse.
- Add TokenTypePartition and the "TABLES" keyword value to isNonReservedKeyword
  so they can serve as identifiers in expression position and after qualifiers.

Closes #480

Author: Ajit Pratap Singh

pkg/sql/parser/clickhouse_table_identifier_test.go

@@ -0,0 +1,104 @@
+// Copyright 2026 GoSQLX Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+
+package parser_test
+
+import (
+	"testing"
+
+	"github.com/ajitpratap0/GoSQLX/pkg/gosqlx"
+	"github.com/ajitpratap0/GoSQLX/pkg/sql/keywords"
+)
+
+// TestClickHouseTableAsIdentifier verifies that the ClickHouse dialect accepts
+// `table` as a column identifier in SELECT lists, function arguments, and
+// GROUP BY clauses. ClickHouse system tables (system.replicas, system.tables,
+// system.parts) all expose a `table` column, so this is a common real-world
+// pattern. Regression test for issue #480.
+func TestClickHouseTableAsIdentifier(t *testing.T) {
+	queries := map[string]string{
+		"replicas_with_table_column": `SELECT
+    database,
+    table,
+    is_leader,
+    is_readonly,
+    is_session_expired,
+    parts_to_check,
+    queue_size,
+    inserts_in_queue,
+    merges_in_queue,
+    absolute_delay,
+    last_queue_update,
+    zookeeper_path
+FROM system.replicas
+ORDER BY absolute_delay DESC`,
+
+		"tables_with_bytes_on_disk": `SELECT
+    database,
+    table,
+    engine,
+    formatReadableSize(bytes_on_disk) AS size,
+    parts,
+    active_parts
+FROM system.tables
+WHERE engine LIKE '%MergeTree%'
+  AND is_temporary = 0
+ORDER BY bytes_on_disk DESC
+LIMIT 10`,
+
+		"tables_with_total_bytes": `SELECT
+    database,
+    table,
+    engine,
+    formatReadableSize(total_bytes) AS size,
+    parts,
+    active_parts
+FROM system.tables
+WHERE engine LIKE '%MergeTree%'
+  AND is_temporary = 0
+ORDER BY total_bytes DESC
+LIMIT 10`,
+
+		"parts_with_concat_table": `SELECT
+    concat(database, '.' ,table) AS table_name,
+    count() AS part_count,
+    max(partition) AS latest_partition,
+    formatReadableSize(sum(bytes_on_disk)) AS total_size
+FROM system.parts
+WHERE active = 1
+  AND database NOT IN ('system')
+GROUP BY database, table
+ORDER BY part_count DESC
+LIMIT 10`,
+
+		"parts_having_count": `SELECT
+    database,
+    table,
+    count() AS parts,
+    formatReadableSize(sum(bytes_on_disk)) AS size
+FROM system.parts
+WHERE active = 1
+  AND database NOT IN ('system')
+GROUP BY database, table
+HAVING parts > 300
+ORDER BY parts DESC`,
+	}
+
+	for name, query := range queries {
+		query := query
+		t.Run(name, func(t *testing.T) {
+			parsed, err := gosqlx.ParseWithDialect(query, keywords.DialectClickHouse)
+			if err != nil {
+				t.Fatalf("ParseWithDialect failed: %v", err)
+			}
+			if parsed == nil {
+				t.Fatal("expected non-nil AST")
+			}
+		})
+	}
+}

pkg/sql/parser/expressions_literal.go

@@ -103,7 +103,7 @@ func (p *Parser) parsePrimaryExpression() (ast.Expression, error) {
 		return funcCall, nil
 	}
 
-	if p.isType(models.TokenTypeIdentifier) || p.isType(models.TokenTypeDoubleQuotedString) || (p.dialect == string(keywords.DialectSQLServer) && p.isNonReservedKeyword()) {
+	if p.isType(models.TokenTypeIdentifier) || p.isType(models.TokenTypeDoubleQuotedString) || ((p.dialect == string(keywords.DialectSQLServer) || p.dialect == string(keywords.DialectClickHouse)) && p.isNonReservedKeyword()) {
 		// Handle identifiers and function calls
 		// Double-quoted strings are treated as identifiers in SQL (e.g., "column_name")
 		// Non-reserved keywords (TARGET, SOURCE, etc.) can also be used as identifiers

pkg/sql/parser/parser.go

@@ -958,14 +958,17 @@ func (p *Parser) isNonReservedKeyword() bool {
 	case models.TokenTypeTarget, models.TokenTypeSource, models.TokenTypeMatched:
 		return true
 	case models.TokenTypeTable, models.TokenTypeIndex, models.TokenTypeView,
-		models.TokenTypeKey, models.TokenTypeColumn, models.TokenTypeDatabase:
+		models.TokenTypeKey, models.TokenTypeColumn, models.TokenTypeDatabase,
+		models.TokenTypePartition:
 		// DDL keywords that are commonly used as quoted identifiers in MySQL (backtick)
-		// and SQL Server (bracket) dialects.
+		// and SQL Server (bracket) dialects, and as plain column names in ClickHouse
+		// system tables (system.parts.partition, system.replicas.table, etc).
 		return true
 	case models.TokenTypeKeyword:
 		// Token may have generic Type; check value for specific keywords
 		switch strings.ToUpper(p.currentToken.Token.Value) {
-		case "TARGET", "SOURCE", "MATCHED", "VALUE", "NAME", "TYPE", "STATUS":
+		case "TARGET", "SOURCE", "MATCHED", "VALUE", "NAME", "TYPE", "STATUS",
+			"TABLES":
 			return true
 		}
 	}