Let EXISTS work subqueries to fix #1904 (#1952)

Co-authored-by: asundukov <asundukov>

src/alasqlparser.jison

@@ -520,9 +520,8 @@ Select
 		    yy.extend($$,$5); yy.extend($$,$6);yy.extend($$,$7);
 		    yy.extend($$,$8); yy.extend($$,$9); yy.extend($$,$10);
 		    $$ = $1;
-/*		    if(yy.exists) $$.exists = yy.exists;
-		    delete yy.exists;
-		    if(yy.queries) $$.queries = yy.queries;
+		    if(yy.exists) $$.exists = yy.exists.slice();
+/*		    if(yy.queries) $$.queries = yy.queries;
 			delete yy.queries;
 */		}
 	| SEARCH SearchSelector* IntoClause SearchFrom?

test/test1904.js

@@ -0,0 +1,45 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 1937: EXISTS in SQL Queries and SET Statements', function () {
+	before(function () {
+		alasql('create database test1937');
+		alasql('use test1937');
+		alasql('DROP TABLE IF EXISTS one');
+		alasql('CREATE TABLE one (a INT)');
+		alasql('INSERT INTO one VALUES (1),(2),(3),(4),(5)');
+	});
+
+	after(function () {
+		alasql('drop database test1937');
+	});
+
+	it('Nested EXISTS in subquery', function (done) {
+		const res = alasql(
+			'SELECT EXISTS(SELECT a FROM one WHERE 0) AS main_exists, * FROM (SELECT EXISTS(SELECT a FROM one) AS sub_exists, a FROM one)'
+		);
+		assert.deepEqual(
+			[
+				{main_exists: false, a: 1, sub_exists: true},
+				{main_exists: false, a: 2, sub_exists: true},
+				{main_exists: false, a: 3, sub_exists: true},
+				{main_exists: false, a: 4, sub_exists: true},
+				{main_exists: false, a: 5, sub_exists: true},
+			],
+			res
+		);
+		done();
+	});
+
+	it('EXISTS in SET statement', function (done) {
+		const res = alasql(
+			`SET @existsLessThan3 = (SELECT EXISTS(SELECT a FROM one WHERE a < 3));
+			SET @existsGreaterThan10 = (SELECT EXISTS(SELECT a FROM one WHERE a > 10));
+			SELECT @existsLessThan3, @existsGreaterThan10;`
+		);
+		assert.deepEqual([{'@existsLessThan3': true, '@existsGreaterThan10': false}], res[2]);
+		done();
+	});
+});