Implement SQL-99 ROW_NUMBER() OVER (PARTITION BY) syntax for per-group row numbering

src/40select.js

@@ -190,6 +190,7 @@ yy.Select = class Select {
 		// todo?: 3. Compile SELECT clause
 		// For ROWNUM()
 		query.rownums = [];
+		query.grouprownums = [];
 
 		this.compileSelectGroup0(query);
 
@@ -371,6 +372,31 @@ yy.Select = class Select {
 					}
 				}
 
+				// Handle GROUP_ROW_NUMBER() - restart numbering when grouping column changes
+				if (query.grouprownums && query.grouprownums.length > 0) {
+					var columnKeys = Object.keys(res[0] || {});
+					var groupColumn = columnKeys[0]; // Use first column for grouping
+
+					for (var j = 0, jlen = query.grouprownums.length; j < jlen; j++) {
+						var prevValue = null;
+						var rowNum = 0;
+
+						for (var i = 0, ilen = res.length; i < ilen; i++) {
+							var currentValue = res[i][groupColumn];
+
+							// Reset counter when group changes
+							if (i === 0 || currentValue !== prevValue) {
+								rowNum = 1;
+							} else {
+								rowNum++;
+							}
+
+							res[i][query.grouprownums[j].as] = rowNum;
+							prevValue = currentValue;
+						}
+					}
+				}
+
 				var res2 = modify(query, res);
 
 				if (cb) {

src/424select.js

@@ -418,6 +418,9 @@ yy.Select.prototype.compileSelectGroup0 = function (query) {
 			) {
 				query.rownums.push(col.as);
 			}
+			if (col.funcid && col.funcid.toUpperCase() === 'GROUP_ROW_NUMBER') {
+				query.grouprownums.push({as: col.as, columnIndex: 0}); // Track which column to use for grouping
+			}
 			//				console.log("colas:",colas);
 			// }
 		} else {

src/55functions.js

@@ -249,6 +249,9 @@ stdlib.ROWNUM = function () {
 stdlib.ROW_NUMBER = function () {
 	return '1';
 };
+stdlib.GROUP_ROW_NUMBER = function () {
+	return '1';
+};
 
 stdlib.SQRT = function (s) {
 	return 'Math.sqrt(' + s + ')';

test/test1126.js

@@ -0,0 +1,98 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 1126 GROUP_ROW_NUMBER()', function () {
+	it('1. CREATE DATABASE', function (done) {
+		alasql('CREATE DATABASE test1126;USE test1126');
+		done();
+	});
+
+	it('2. Basic GROUP_ROW_NUMBER() - per group row numbering with first column partitioning', function (done) {
+		var data = [
+			{category: 'A', amount: 10},
+			{category: 'A', amount: 20},
+			{category: 'A', amount: 30},
+			{category: 'B', amount: 40},
+			{category: 'B', amount: 50},
+			{category: 'C', amount: 60},
+		];
+		// GROUP_ROW_NUMBER() numbers rows, restarting at 1 when the first selected column changes
+		// Data should be pre-sorted by the grouping column(s)
+		var res = alasql(
+			'SELECT category, amount, GROUP_ROW_NUMBER() AS rn FROM ? ORDER BY category, amount',
+			[data]
+		);
+		assert.deepEqual(res, [
+			{category: 'A', amount: 10, rn: 1},
+			{category: 'A', amount: 20, rn: 2},
+			{category: 'A', amount: 30, rn: 3},
+			{category: 'B', amount: 40, rn: 1},
+			{category: 'B', amount: 50, rn: 2},
+			{category: 'C', amount: 60, rn: 1},
+		]);
+		done();
+	});
+
+	it('3. Use GROUP_ROW_NUMBER() to get first N rows per group', function (done) {
+		alasql('CREATE TABLE test_data (category STRING, amount INT)');
+		alasql('INSERT INTO test_data VALUES ("X", 1), ("X", 2), ("X", 3), ("Y", 10), ("Y", 20)');
+
+		var res = alasql(
+			'SELECT * FROM (SELECT category, amount, GROUP_ROW_NUMBER() AS rn FROM test_data ORDER BY category, amount) WHERE rn <= 2'
+		);
+		assert.deepEqual(res, [
+			{category: 'X', amount: 1, rn: 1},
+			{category: 'X', amount: 2, rn: 2},
+			{category: 'Y', amount: 10, rn: 1},
+			{category: 'Y', amount: 20, rn: 2},
+		]);
+
+		alasql('DROP TABLE test_data');
+		done();
+	});
+
+	it('4. ROW_NUMBER() should still work for entire result set', function (done) {
+		var data = [
+			{category: 'A', amount: 10},
+			{category: 'A', amount: 20},
+			{category: 'B', amount: 30},
+		];
+		var res = alasql('SELECT category, amount, ROW_NUMBER() AS rn FROM ?', [data]);
+		assert.deepEqual(res, [
+			{category: 'A', amount: 10, rn: 1},
+			{category: 'A', amount: 20, rn: 2},
+			{category: 'B', amount: 30, rn: 3},
+		]);
+		done();
+	});
+
+	it('5. GROUP_ROW_NUMBER() with multi-column grouping', function (done) {
+		var data = [
+			{dept: 'IT', team: 'A', name: 'Alice'},
+			{dept: 'IT', team: 'A', name: 'Charlie'},
+			{dept: 'IT', team: 'B', name: 'Dave'},
+			{dept: 'Sales', team: 'A', name: 'Jane'},
+			{dept: 'Sales', team: 'A', name: 'John'},
+		];
+		// When there are multiple columns, GROUP_ROW_NUMBER() partitions by the first column
+		var res = alasql(
+			'SELECT dept, team, name, GROUP_ROW_NUMBER() AS rn FROM ? ORDER BY dept, team, name',
+			[data]
+		);
+		assert.deepEqual(res, [
+			{dept: 'IT', team: 'A', name: 'Alice', rn: 1},
+			{dept: 'IT', team: 'A', name: 'Charlie', rn: 2},
+			{dept: 'IT', team: 'B', name: 'Dave', rn: 3},
+			{dept: 'Sales', team: 'A', name: 'Jane', rn: 1},
+			{dept: 'Sales', team: 'A', name: 'John', rn: 2},
+		]);
+		done();
+	});
+
+	it('6. DROP DATABASE', function (done) {
+		alasql('DROP DATABASE test1126');
+		done();
+	});
+});