Test coverage for JOIN with duplicate column names to close #547 (#2347)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: mathiasrw <[email protected]>

Author: Copilot

test/test547.js

@@ -0,0 +1,154 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+// Test for issue #547 - JOIN should return fields from both tables
+
+describe('Test 547 - JOIN with duplicate column names', function () {
+	after(function () {
+		// Restore default joinstar option
+		alasql.options.joinstar = 'overwrite';
+	});
+
+	it('1. OVERWRITE mode (default) - later columns overwrite earlier ones', function () {
+		alasql.options.joinstar = 'overwrite';
+
+		var data = [{dep: 'A', qt: 10, price: 5, extra: 1}];
+		var data2 = [{dep: 'B', qt: 2, price: 5}];
+
+		// JOIN without ON clause produces cartesian product (1 row × 1 row = 1 row)
+		var res = alasql('SELECT * FROM ? as a JOIN ? as b', [data, data2]);
+
+		// With overwrite mode, duplicate columns (dep, qt, price) should be overwritten by b's values
+		// Non-duplicate column (extra) should be preserved from a
+		assert.deepEqual(res, [{dep: 'B', qt: 2, price: 5, extra: 1}]);
+	});
+
+	it('2. JSON mode - nested objects by table alias', function () {
+		alasql.options.joinstar = 'json';
+
+		var data = [{dep: 'A', qt: 10, price: 5, extra: 1}];
+		var data2 = [{dep: 'B', qt: 2, price: 5}];
+
+		// JOIN without ON clause produces cartesian product (1 row × 1 row = 1 row)
+		var res = alasql('SELECT * FROM ? as a JOIN ? as b', [data, data2]);
+
+		// With json mode, each table's data should be nested under its alias
+		assert.deepEqual(res, [
+			{
+				a: {dep: 'A', qt: 10, price: 5, extra: 1},
+				b: {dep: 'B', qt: 2, price: 5},
+			},
+		]);
+	});
+
+	it('3. UNDERSCORE mode - prefix columns with table alias', function () {
+		alasql.options.joinstar = 'underscore';
+
+		var data = [{dep: 'A', qt: 10, price: 5, extra: 1}];
+		var data2 = [{dep: 'B', qt: 2, price: 5}];
+
+		// JOIN without ON clause produces cartesian product (1 row × 1 row = 1 row)
+		var res = alasql('SELECT * FROM ? as a JOIN ? as b', [data, data2]);
+
+		// With underscore mode, columns should be prefixed with their table alias
+		assert.deepEqual(res, [
+			{
+				a_dep: 'A',
+				a_qt: 10,
+				a_price: 5,
+				a_extra: 1,
+				b_dep: 'B',
+				b_qt: 2,
+				b_price: 5,
+			},
+		]);
+	});
+
+	it('4. OVERWRITE mode with CROSS JOIN', function () {
+		alasql.options.joinstar = 'overwrite';
+
+		var data = [{a: 1}, {a: 2}];
+		var data2 = [{a: 10}, {a: 20}];
+
+		var res = alasql('SELECT * FROM ? as one, ? as two', [data, data2]);
+
+		// Cartesian product with overwrite - column 'a' from 'two' overwrites 'a' from 'one'
+		assert.deepEqual(res, [{a: 10}, {a: 20}, {a: 10}, {a: 20}]);
+	});
+
+	it('5. JSON mode with CROSS JOIN', function () {
+		alasql.options.joinstar = 'json';
+
+		var data = [{a: 1}, {a: 2}];
+		var data2 = [{a: 10}, {a: 20}];
+
+		var res = alasql('SELECT * FROM ? as one, ? as two', [data, data2]);
+
+		// Cartesian product with nested objects
+		assert.deepEqual(res, [
+			{one: {a: 1}, two: {a: 10}},
+			{one: {a: 1}, two: {a: 20}},
+			{one: {a: 2}, two: {a: 10}},
+			{one: {a: 2}, two: {a: 20}},
+		]);
+	});
+
+	it('6. UNDERSCORE mode with CROSS JOIN', function () {
+		alasql.options.joinstar = 'underscore';
+
+		var data = [{a: 1}, {a: 2}];
+		var data2 = [{a: 10}, {a: 20}];
+
+		var res = alasql('SELECT * FROM ? as one, ? as two', [data, data2]);
+
+		// Cartesian product with prefixed columns
+		assert.deepEqual(res, [
+			{one_a: 1, two_a: 10},
+			{one_a: 1, two_a: 20},
+			{one_a: 2, two_a: 10},
+			{one_a: 2, two_a: 20},
+		]);
+	});
+
+	it('7. Mixed columns - some shared, some unique', function () {
+		alasql.options.joinstar = 'json';
+
+		var data = [{id: 1, name: 'Alice', age: 30}];
+		var data2 = [{id: 2, name: 'Bob', salary: 50000}];
+
+		// JOIN without ON clause produces cartesian product (1 row × 1 row = 1 row)
+		var res = alasql('SELECT * FROM ? as employees JOIN ? as contractors', [data, data2]);
+
+		// Both tables have 'id' and 'name', but different other columns
+		assert.deepEqual(res, [
+			{
+				employees: {id: 1, name: 'Alice', age: 30},
+				contractors: {id: 2, name: 'Bob', salary: 50000},
+			},
+		]);
+	});
+
+	it('8. UNDERSCORE mode with mixed columns', function () {
+		alasql.options.joinstar = 'underscore';
+
+		var data = [{id: 1, name: 'Alice', age: 30}];
+		var data2 = [{id: 2, name: 'Bob', salary: 50000}];
+
+		// JOIN without ON clause produces cartesian product (1 row × 1 row = 1 row)
+		var res = alasql('SELECT * FROM ? as employees JOIN ? as contractors', [data, data2]);
+
+		// All columns prefixed with table alias
+		assert.deepEqual(res, [
+			{
+				employees_id: 1,
+				employees_name: 'Alice',
+				employees_age: 30,
+				contractors_id: 2,
+				contractors_name: 'Bob',
+				contractors_salary: 50000,
+			},
+		]);
+	});
+});