Fix #1109 (#1872)

src/833xlsx.js

@@ -90,10 +90,14 @@ alasql.into.XLSX = function (filename, opts, data, columns, cb) {
 		var dataLength = Object.keys(data).length;
 
 		// Generate columns if they are not defined
-		if ((!columns || columns.length == 0) && dataLength > 0) {
-			columns = Object.keys(data[0]).map(function (columnid) {
-				return {columnid: columnid};
-			});
+		if (!columns || columns.length == 0) {
+			if (dataLength > 0) {
+				columns = Object.keys(data[0]).map(function (columnid) {
+					return {columnid: columnid};
+				});
+			} else {
+				columns = [];
+			}
 		}
 
 		var cells = {};

test/test1109.js

@@ -0,0 +1,26 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 1109 - Export empty tables to excel sheets', function () {
+	const test = '1109';
+
+	before(function () {
+		alasql('create database test' + test);
+		alasql('use test' + test);
+	});
+
+	after(function () {
+		alasql('drop database test' + test);
+	});
+
+	it('A) Export empty tables to excel sheets', function () {
+		var res = [];
+		var opts = [{sheetid: 'a'}, {sheetid: 'b'}];
+		res.push(
+			alasql('SELECT INTO XLSX("' + __dirname + '/restest1109.xlsx",?) FROM ?', [opts, [[], []]])
+		);
+		assert.deepEqual(res, [1]);
+	});
+});