Improve test coverage for scalar subqueries to close #1967 (#2397)

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

Author: Copilot

test/test1967.js

@@ -0,0 +1,151 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test - Scalar Subquery Support', function () {
+	const test = 'scalarsubquery';
+
+	before(function () {
+		alasql('create database test' + test);
+		alasql('use test' + test);
+	});
+
+	after(function () {
+		alasql('drop database test' + test);
+	});
+
+	it('A) Scalar subquery in SELECT clause - basic', function () {
+		alasql('CREATE TABLE products (id INT, name STRING, price INT)');
+		alasql(
+			'INSERT INTO products VALUES (1, "Widget", 10), (2, "Gadget", 20), (3, "Doohickey", 30)'
+		);
+
+		var res = alasql(
+			'SELECT id, name, price, (SELECT MAX(price) FROM products) as max_price FROM products'
+		);
+
+		assert.deepEqual(res, [
+			{id: 1, name: 'Widget', price: 10, max_price: 30},
+			{id: 2, name: 'Gadget', price: 20, max_price: 30},
+			{id: 3, name: 'Doohickey', price: 30, max_price: 30},
+		]);
+	});
+
+	it('B) Scalar subquery in SELECT clause - with aggregate functions', function () {
+		var res = alasql(
+			'SELECT id, name, price, (SELECT AVG(price) FROM products) as avg_price, (SELECT MIN(price) FROM products) as min_price FROM products'
+		);
+
+		assert.deepEqual(res, [
+			{id: 1, name: 'Widget', price: 10, avg_price: 20, min_price: 10},
+			{id: 2, name: 'Gadget', price: 20, avg_price: 20, min_price: 10},
+			{id: 3, name: 'Doohickey', price: 30, avg_price: 20, min_price: 10},
+		]);
+	});
+
+	it('C) Scalar subquery in WHERE clause', function () {
+		var res = alasql('SELECT * FROM products WHERE price > (SELECT AVG(price) FROM products)');
+
+		assert.deepEqual(res, [{id: 3, name: 'Doohickey', price: 30}]);
+	});
+
+	it('D) Scalar subquery in WHERE clause - with comparison operators', function () {
+		var res = alasql('SELECT * FROM products WHERE price = (SELECT MAX(price) FROM products)');
+
+		assert.deepEqual(res, [{id: 3, name: 'Doohickey', price: 30}]);
+	});
+
+	it('E) Correlated scalar subquery - SUM aggregate', function () {
+		alasql('CREATE TABLE customers (id INT, name STRING, income INT)');
+		alasql(
+			'INSERT INTO customers VALUES (1, "Alice", 50000), (2, "Bob", 60000), (3, "Charlie", 70000)'
+		);
+		alasql('CREATE TABLE orders (customer_id INT, amount INT)');
+		alasql('INSERT INTO orders VALUES (1, 100), (1, 200), (2, 150), (2, 250), (3, 300), (3, 400)');
+
+		var res = alasql(
+			'SELECT c.id, c.name, (SELECT SUM(amount) FROM orders o WHERE o.customer_id = c.id) as total_orders FROM customers c'
+		);
+
+		assert.deepEqual(res, [
+			{id: 1, name: 'Alice', total_orders: 300},
+			{id: 2, name: 'Bob', total_orders: 400},
+			{id: 3, name: 'Charlie', total_orders: 700},
+		]);
+	});
+
+	it('F) Correlated scalar subquery - COUNT aggregate', function () {
+		var res = alasql(
+			'SELECT c.id, c.name, (SELECT COUNT(*) FROM orders o WHERE o.customer_id = c.id) as order_count FROM customers c'
+		);
+
+		assert.deepEqual(res, [
+			{id: 1, name: 'Alice', order_count: 2},
+			{id: 2, name: 'Bob', order_count: 2},
+			{id: 3, name: 'Charlie', order_count: 2},
+		]);
+	});
+
+	it('G) Correlated scalar subquery - AVG aggregate', function () {
+		var res = alasql(
+			'SELECT c.id, c.name, (SELECT AVG(amount) FROM orders o WHERE o.customer_id = c.id) as avg_order FROM customers c'
+		);
+
+		assert.deepEqual(res, [
+			{id: 1, name: 'Alice', avg_order: 150},
+			{id: 2, name: 'Bob', avg_order: 200},
+			{id: 3, name: 'Charlie', avg_order: 350},
+		]);
+	});
+
+	it('H) Multiple scalar subqueries in SELECT clause', function () {
+		var res = alasql(`
+			SELECT c.id, c.name, 
+				(SELECT SUM(amount) FROM orders o WHERE o.customer_id = c.id) as sum_amt, 
+				(SELECT AVG(amount) FROM orders o WHERE o.customer_id = c.id) as avg_amt, 
+				(SELECT COUNT(*) FROM orders o WHERE o.customer_id = c.id) as cnt 
+			FROM customers c 
+			WHERE c.id = 1
+		`);
+
+		assert.deepEqual(res, [{id: 1, name: 'Alice', sum_amt: 300, avg_amt: 150, cnt: 2}]);
+	});
+
+	it('I) Scalar subquery with WHERE condition in subquery', function () {
+		var res = alasql(
+			'SELECT * FROM customers WHERE income > (SELECT AVG(income) FROM customers WHERE id > 1)'
+		);
+
+		assert.deepEqual(res, [{id: 3, name: 'Charlie', income: 70000}]);
+	});
+
+	it('J) Scalar subquery in complex WHERE condition', function () {
+		alasql('CREATE TABLE stats (category STRING, avg_val INT)');
+		alasql('INSERT INTO stats VALUES ("high", 65000), ("low", 55000)');
+
+		var res = alasql(
+			'SELECT * FROM customers WHERE income > (SELECT avg_val FROM stats WHERE category = "high")'
+		);
+
+		assert.deepEqual(res, [{id: 3, name: 'Charlie', income: 70000}]);
+	});
+
+	it('K) Scalar subquery returns 0 for SUM when no rows match', function () {
+		var res = alasql(
+			'SELECT c.id, c.name, (SELECT SUM(amount) FROM orders o WHERE o.customer_id = 999) as no_orders FROM customers c WHERE c.id = 1'
+		);
+
+		// Note: In AlaSQL, SUM returns 0 when no rows match.
+		// This differs from standard SQL where SUM typically returns NULL for empty result sets.
+		assert.deepEqual(res, [{id: 1, name: 'Alice', no_orders: 0}]);
+	});
+
+	it('L) Scalar subquery in arithmetic expression', function () {
+		var res = alasql(
+			'SELECT id, name, price, price - (SELECT AVG(price) FROM products) as price_diff FROM products WHERE id = 1'
+		);
+
+		assert.deepEqual(res, [{id: 1, name: 'Widget', price: 10, price_diff: -10}]);
+	});
+});