Let RECORDSET return empty data if no rows to fix #1547 (#2294)

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

Author: 3 people

src/40select.js

@@ -501,6 +501,13 @@ function modify(query, res) {
 		} else {
 			// Cannot recognize columns
 			columns = [];
+			if (query && query.sources) {
+				query.sources.forEach(source => {
+					if (source && source.columns && Array.isArray(source.columns)) {
+						columns = columns.concat(source.columns);
+					}
+				});
+			}
 		}
 	}
 

test/test1547.js

@@ -0,0 +1,41 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 1547 - Empty recordset', function () {
+	const test = '1547';
+
+	before(function () {
+		alasql('create database test' + test);
+		alasql('use test' + test);
+	});
+
+	after(function () {
+		alasql('drop database test' + test);
+	});
+
+	it('Returns columns for empty recordset', function () {
+		alasql('create table one (a int)');
+		alasql('insert into one values (1),(2),(3),(4),(5)');
+		let res = alasql('recordset of select * from one where a = 999');
+
+		// Verify that columns are returned even when there are no rows
+		assert.strictEqual(res.columns.length, 1, 'Should have 1 column');
+		assert.strictEqual(res.columns[0].columnid, 'a', 'Column should be named "a"');
+		assert.strictEqual(res.data.length, 0, 'Data should be empty');
+	});
+
+	it('Returns multiple columns for empty recordset', function () {
+		alasql('create table multi (id int, name varchar(50), amount double)');
+		alasql('insert into multi values (1, "test", 1.5), (2, "test2", 2.5)');
+		let res = alasql('recordset of select * from multi where id = 999');
+
+		// Verify that all columns are returned even when there are no rows
+		assert.strictEqual(res.columns.length, 3, 'Should have 3 columns');
+		assert.strictEqual(res.columns[0].columnid, 'id', 'First column should be "id"');
+		assert.strictEqual(res.columns[1].columnid, 'name', 'Second column should be "name"');
+		assert.strictEqual(res.columns[2].columnid, 'amount', 'Third column should be "amount"');
+		assert.strictEqual(res.data.length, 0, 'Data should be empty');
+	});
+});