Fix GROUP BY with aliased expressions (CASE, functions)

.prettierignore

@@ -13,3 +13,7 @@ src/97saveas.js
 modules/
 
 test/test238.json
+
+build/
+
+test/lib/

src/424select.js

@@ -473,6 +473,31 @@ yy.Select.prototype.compileSelect2 = function (query, params) {
 
 yy.Select.prototype.compileSelectGroup0 = function (query) {
 	var self = this;
+
+	// Optimization: Build lookup structures upfront to avoid O(n*m) complexity in the main loop
+	// Only build these if GROUP BY exists, as they're only used for alias resolution
+	var groupByAliasMap = null;
+	var selectColumnNames = null;
+
+	if (self.group) {
+		// Build map of GROUP BY columns that reference aliases (for O(1) lookup)
+		groupByAliasMap = {};
+		self.group.forEach(function (gp, idx) {
+			if (gp instanceof yy.Column && gp.columnid && !gp.tableid) {
+				groupByAliasMap[gp.columnid] = idx;
+			}
+		});
+
+		// Build set of actual column names in SELECT to distinguish pure aliases from column renames
+		// This prevents incorrect replacement of "GROUP BY b" when "SELECT a AS b, b AS c" exists
+		selectColumnNames = {};
+		self.columns.forEach(function (col) {
+			if (col instanceof yy.Column && col.columnid) {
+				selectColumnNames[col.columnid] = true;
+			}
+		});
+	}
+
 	self.columns.forEach(function (col, idx) {
 		if (!(col instanceof yy.Column && col.columnid === '*')) {
 			var colas;
@@ -493,12 +518,35 @@ yy.Select.prototype.compileSelectGroup0 = function (query) {
 			col.nick = colas;
 
 			if (self.group) {
+				// Match GROUP BY columns to SELECT columns by columnid and tableid (for real columns)
 				var groupIdx = self.group.findIndex(function (gp) {
 					return gp.columnid === col.columnid && gp.tableid === col.tableid;
 				});
 				if (groupIdx > -1) {
 					self.group[groupIdx].nick = colas;
 				}
+
+				// Also match GROUP BY columns that reference SELECT column aliases
+				// This handles cases like: SELECT CASE ... END AS age_group ... GROUP BY age_group
+				// Only apply if:
+				// 1. The SELECT column has an alias
+				// 2. That alias matches a GROUP BY column name
+				// 3. The alias is NOT an actual column name (pure alias, not renaming)
+				if (
+					col.as &&
+					groupByAliasMap &&
+					groupByAliasMap.hasOwnProperty(col.as) &&
+					!selectColumnNames[col.as]
+				) {
+					var aliasGroupIdx = groupByAliasMap[col.as];
+					// Replace the GROUP BY column reference with a deep copy of the SELECT expression
+					// We use deep cloning to ensure nested objects (like CASE whens/elses) are copied
+					var groupExpr = cloneDeep(col);
+					// Clear SELECT-specific properties that shouldn't be in GROUP BY
+					delete groupExpr.as;
+					groupExpr.nick = colas;
+					self.group[aliasGroupIdx] = groupExpr;
+				}
 			}
 
 			if (

test/test1146.js

@@ -0,0 +1,155 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+describe('Test 2361 - GROUP BY with CASE expression alias', function () {
+	const test = '2361';
+
+	before(function () {
+		alasql('create database test' + test);
+		alasql('use test' + test);
+	});
+
+	after(function () {
+		alasql('drop database test' + test);
+	});
+
+	it('A) GROUP BY with CASE WHEN aliased expression', function () {
+		// Create test data with ages
+		var data = [{age: 25}, {age: 26}, {age: 35}, {age: 36}, {age: 45}, {age: 55}];
+
+		var result = alasql(
+			`SELECT 
+				CASE 
+					WHEN age BETWEEN 20 AND 29 THEN '20-29'
+					WHEN age BETWEEN 30 AND 39 THEN '30-39'
+					WHEN age BETWEEN 40 AND 49 THEN '40-49'
+					WHEN age BETWEEN 50 AND 59 THEN '50-59'
+					ELSE '60+'
+				END AS age_group,
+				COUNT(*) AS customer_count
+			FROM ?
+			GROUP BY age_group
+			ORDER BY age_group`,
+			[data]
+		);
+
+		var expected = [
+			{age_group: '20-29', customer_count: 2},
+			{age_group: '30-39', customer_count: 2},
+			{age_group: '40-49', customer_count: 1},
+			{age_group: '50-59', customer_count: 1},
+		];
+
+		assert.deepEqual(result, expected);
+	});
+
+	it('B) GROUP BY with CASE WHEN and ELSE clause', function () {
+		var data = [{age: 10}, {age: 20}, {age: 30}, {age: 100}];
+
+		var result = alasql(
+			`SELECT 
+				CASE 
+					WHEN age BETWEEN 0 AND 9 THEN '0-9'
+					WHEN age BETWEEN 10 AND 19 THEN '10-19'
+					WHEN age BETWEEN 20 AND 29 THEN '20-29'
+					ELSE '30+'
+				END AS age_group
+			FROM ? 
+			GROUP BY age_group`,
+			[data]
+		);
+
+		// Should return three unique groups, not just '30+'
+		var expected = [{age_group: '10-19'}, {age_group: '20-29'}, {age_group: '30+'}];
+
+		assert.deepEqual(result.sort(), expected.sort());
+	});
+
+	it('C) GROUP BY with function expression alias', function () {
+		var data = [{name: 'Alice'}, {name: 'alice'}, {name: 'Bob'}, {name: 'bob'}];
+
+		var result = alasql(
+			`SELECT 
+				UPPER(name) AS upper_name,
+				COUNT(*) AS cnt
+			FROM ?
+			GROUP BY upper_name
+			ORDER BY upper_name`,
+			[data]
+		);
+
+		var expected = [
+			{upper_name: 'ALICE', cnt: 2},
+			{upper_name: 'BOB', cnt: 2},
+		];
+
+		assert.deepEqual(result, expected);
+	});
+
+	it('D) GROUP BY with multiple CASE expressions', function () {
+		var data = [
+			{age: 25, score: 85},
+			{age: 26, score: 90},
+			{age: 35, score: 85},
+			{age: 36, score: 90},
+		];
+
+		var result = alasql(
+			`SELECT 
+				CASE 
+					WHEN age BETWEEN 20 AND 29 THEN '20-29'
+					ELSE '30+'
+				END AS age_group,
+				CASE 
+					WHEN score >= 90 THEN 'High'
+					ELSE 'Low'
+				END AS score_group,
+				COUNT(*) AS cnt
+			FROM ?
+			GROUP BY age_group, score_group
+			ORDER BY age_group, score_group`,
+			[data]
+		);
+
+		var expected = [
+			{age_group: '20-29', score_group: 'High', cnt: 1},
+			{age_group: '20-29', score_group: 'Low', cnt: 1},
+			{age_group: '30+', score_group: 'High', cnt: 1},
+			{age_group: '30+', score_group: 'Low', cnt: 1},
+		];
+
+		assert.deepEqual(result, expected);
+	});
+
+	it('E) GROUP BY with WHERE and CASE expression alias', function () {
+		var data = [
+			{age: 25, active: true},
+			{age: 26, active: false},
+			{age: 35, active: true},
+			{age: 36, active: true},
+		];
+
+		var result = alasql(
+			`SELECT 
+				CASE 
+					WHEN age BETWEEN 20 AND 29 THEN '20-29'
+					ELSE '30+'
+				END AS age_group,
+				COUNT(*) AS cnt
+			FROM ?
+			WHERE active = true
+			GROUP BY age_group
+			ORDER BY age_group`,
+			[data]
+		);
+
+		var expected = [
+			{age_group: '20-29', cnt: 1},
+			{age_group: '30+', cnt: 2},
+		];
+
+		assert.deepEqual(result, expected);
+	});
+});