fix RECORDSET returning empty columns if there's no matched rows issu…

src/40select.js

@@ -468,6 +468,12 @@ function modify(query, res) {
 		} else {
 			// Cannot recognize columns
 			columns = [];
+			if (query && query.sources) {
+				query.sources.forEach((source) => {
+					if(source?.columns?.columnid != null)
+						columns = columns.concat({columnid:source?.columns?.columnid});
+				})
+			}
 		}
 	}
 

test/test1547.js

@@ -0,0 +1,64 @@
+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');
+		assert.deepEqual(res, {
+			columns: [
+				{
+					columnid: 'a',
+				},
+			],
+			data: [],
+		});
+
+		/* assert(
+			(() => {
+				const testdata = {
+					columns: [
+						{
+							columnid: 'a',
+						},
+					],
+					data: [],
+				};
+
+				if (
+					res.columns.length !== testdata.columns.length ||
+					res.data.length !== testdata.data.length
+				) {
+					return false;
+				} else {
+					let cols = res.columns;
+
+					for (let col of cols) {
+						let index = testdata.columns.findIndex((c) => c.columnid === col.columnid);
+
+						if (index === -1) {
+							return false;
+						}
+					}
+
+					return true;
+				}
+			})(),
+			'Response should not have missing coloumns'
+		);*/
+	});
+});