Fix DISTINCT with object values in SELECT and SEARCH queries

src/38query.js

@@ -376,7 +376,9 @@ function doDistinct(query) {
 		for (var i = 0, ilen = query.data.length; i < ilen; i++) {
 			var uix = keys
 				.map(function (k) {
-					return query.data[i][k];
+					var val = query.data[i][k];
+					// Properly serialize objects for comparison
+					return typeof val === 'object' ? JSON.stringify(val) : val;
 				})
 				.join('`');
 			uniq[uix] = query.data[i];

src/40select.js

@@ -469,6 +469,11 @@ function modify(query, res) {
 				ar.push(res[i][key]);
 			}
 
+			// Apply DISTINCT if specified
+			if (query.distinct) {
+				ar = alasql.utils.distinctArray(ar);
+			}
+
 			return ar;
 
 		case 'MATRIX':

test/test167B.js

@@ -0,0 +1,83 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 167B - SEARCH DISTINCT and SELECT DISTINCT functions', function () {
+	it('1. Basic DISTINCT comparison', () => {
+		var data = [{a: 1}, {a: 2}, {a: 1}];
+
+		var res1 = alasql('SELECT * FROM ?', [data]);
+		var res2 = alasql('SELECT DISTINCT * FROM ?', [data]);
+		var res3 = alasql('SELECT COLUMN DISTINCT _ FROM ?', [data]);
+		var res4 = alasql('SEARCH DISTINCT(/) FROM ?', [data]);
+
+		console.log('res1 (SELECT *):', JSON.stringify(res1));
+		console.log('res2 (SELECT DISTINCT *):', JSON.stringify(res2));
+		console.log('res3 (SELECT COLUMN DISTINCT _):', JSON.stringify(res3));
+		console.log('res4 (SEARCH DISTINCT(/)):', JSON.stringify(res4));
+
+		// res1 should have all 3 items
+		assert.equal(res1.length, 3);
+
+		// res2, res3, res4 should all have 2 distinct items
+		assert.equal(res2.length, 2, 'SELECT DISTINCT * should return 2 items');
+		assert.equal(res3.length, 2, 'SELECT COLUMN DISTINCT _ should return 2 items');
+		assert.equal(res4.length, 2, 'SEARCH DISTINCT(/) should return 2 items');
+	});
+
+	it('2. DISTINCT with different middle value (issue b)', () => {
+		var data = [{a: 1}, {b: 2}, {a: 1}];
+
+		var res3 = alasql('SELECT COLUMN DISTINCT _ FROM ?', [data]);
+		var res4 = alasql('SEARCH DISTINCT(/) FROM ?', [data]);
+
+		console.log('res3 (SELECT COLUMN DISTINCT _) with mixed data:', JSON.stringify(res3));
+		console.log('res4 (SEARCH DISTINCT(/)) with mixed data:', JSON.stringify(res4));
+
+		// Should return 2 distinct objects: {a:1} and {b:2}
+		assert.equal(res3.length, 2, 'SELECT COLUMN DISTINCT _ should return 2 items');
+		assert.equal(res4.length, 2, 'SEARCH DISTINCT(/) should return 2 items');
+
+		// Check that we have both distinct objects
+		var hasA1 = res3.some(function (item) {
+			return item.a === 1 && !item.b;
+		});
+		var hasB2 = res3.some(function (item) {
+			return item.b === 2 && !item.a;
+		});
+
+		assert(hasA1, 'Result should contain {a:1}');
+		assert(hasB2, 'Result should contain {b:2}');
+	});
+
+	it('3. SEARCH DISTINCT vs SELECT DISTINCT consistency', () => {
+		var data = [{a: 1}, {b: 2}, {a: 1}];
+
+		var res2 = alasql('SELECT DISTINCT * FROM ?', [data]);
+		var res4 = alasql('SEARCH DISTINCT(/) FROM ?', [data]);
+
+		console.log('res2 (SELECT DISTINCT *):', JSON.stringify(res2));
+		console.log('res4 (SEARCH DISTINCT(/)):', JSON.stringify(res4));
+
+		// Results should be the same
+		assert.deepEqual(
+			res2,
+			res4,
+			'SELECT DISTINCT * and SEARCH DISTINCT(/) should produce same results'
+		);
+	});
+
+	it('4. SELECT COLUMN DISTINCT _ with arrays', () => {
+		var data = [1, 2, 1, 3, 2];
+
+		var res = alasql('SELECT COLUMN DISTINCT _ FROM ?', [data]);
+		console.log('SELECT COLUMN DISTINCT _ from array:', JSON.stringify(res));
+
+		// Should return distinct values: [1, 2, 3]
+		assert.equal(res.length, 3, 'Should return 3 distinct values');
+		assert(res.includes(1), 'Should include 1');
+		assert(res.includes(2), 'Should include 2');
+		assert(res.includes(3), 'Should include 3');
+	});
+});