Fix CAST/CONVERT of NULL returning 0, false or "undefined" to close #1208

src/59convert.js

@@ -64,6 +64,9 @@ function structuredDate(unFormattedDate) {
  Convert one type to another
  */
 alasql.stdfn.CONVERT = function (value, args) {
+	// CAST/CONVERT of NULL is NULL for every target type (AlaSQL uses undefined for NULL)
+	if (value == null) return undefined;
+
 	var val = value;
 	var udbtypeid = args.dbtypeid?.toUpperCase();
 

test/test1208.js

@@ -0,0 +1,128 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+let testId = '1208'; // CAST / CONVERT of NULL should stay NULL (undefined)
+
+describe(`Test ${testId} - CAST and CONVERT of NULL`, function () {
+	const data = [
+		{
+			FILTER_COL: 'COL1',
+			TEST_COL2: 'COL2',
+			TEST_COL3: 'UNIQ VAL 3',
+			TOTAL_COST: 1500,
+			'DYNAMIC COL1': null,
+		},
+		{
+			FILTER_COL: 'COL1',
+			TEST_COL2: 'COL2',
+			TEST_COL3: 'UNIQ VAL 33',
+			TOTAL_COST: 100,
+			'DYNAMIC COL2': null,
+			'DYNAMIC COL3': null,
+		},
+		{
+			FILTER_COL: 'COL3',
+			TEST_COL2: 'UNIQ VAL 222',
+			TEST_COL3: 'UNIQ VAL 333',
+			TOTAL_COST: 100,
+			'DYNAMIC COL2': null,
+			'DYNAMIC COL5': null,
+		},
+		{
+			FILTER_COL: 'COL3',
+			TEST_COL2: 'UNIQ VAL 2222',
+			TEST_COL3: 'UNIQ VAL 3333',
+			TOTAL_COST: 100,
+			'DYNAMIC COL4': null,
+			'DYNAMIC COL5': null,
+		},
+	];
+
+	const avgs = ['DYNAMIC COL1', 'DYNAMIC COL2', 'DYNAMIC COL3', 'DYNAMIC COL4', 'DYNAMIC COL5']
+		.map((c, i) => `AVG(CAST(\`${c}\` AS NUMBER)) AS a${i + 1}`)
+		.join(', ');
+	const noAvg = {a1: undefined, a2: undefined, a3: undefined, a4: undefined, a5: undefined};
+
+	it('A) AVG(CAST(x AS NUMBER)) over NULL values is undefined, not 0 (issue example 1)', function () {
+		const res = alasql(
+			`SELECT TEST_COL2, SUM(TOTAL_COST) AS cost, ${avgs}
+				FROM ? WHERE FILTER_COL = ? GROUP BY TEST_COL2`,
+			[data, 'COL1']
+		);
+		assert.deepStrictEqual(res, [{TEST_COL2: 'COL2', cost: 1600, ...noAvg}]);
+	});
+
+	it('B) AVG(CAST(x AS NUMBER)) over NULL values is undefined, not 0 (issue example 2)', function () {
+		const res = alasql(
+			`SELECT TEST_COL3, SUM(TOTAL_COST) AS cost, ${avgs}
+				FROM ? WHERE FILTER_COL = ? GROUP BY TEST_COL3`,
+			[data, 'COL3']
+		);
+		assert.deepStrictEqual(res, [
+			{TEST_COL3: 'UNIQ VAL 333', cost: 100, ...noAvg},
+			{TEST_COL3: 'UNIQ VAL 3333', cost: 100, ...noAvg},
+		]);
+	});
+
+	it('C) CAST(NULL AS <type>) returns undefined for every type', function () {
+		const types = [
+			'NUMBER',
+			'INT',
+			'INTEGER',
+			'SMALLINT',
+			'BIGINT',
+			'FLOAT',
+			'DECIMAL(10,2)',
+			'NUMERIC',
+			'MONEY',
+			'STRING',
+			'VARCHAR(10)',
+			'NVARCHAR',
+			'CHAR(3)',
+			'BOOLEAN',
+			'DATE',
+			'DATETIME',
+			'JSON',
+		];
+		const res = types.map(type => alasql(`VALUE OF SELECT CAST(NULL AS ${type})`));
+		assert.deepStrictEqual(
+			res,
+			types.map(() => undefined)
+		);
+	});
+
+	it('D) CAST of a column holding null or missing stays undefined', function () {
+		const res = alasql(
+			`SELECT CAST(a AS NUMBER) AS n, CAST(a AS INT) AS i, CAST(a AS STRING) AS s,
+				CAST(a AS BOOLEAN) AS b, CAST(a AS DATE) AS d FROM ?`,
+			[[{a: null}, {}]]
+		);
+		const empty = {n: undefined, i: undefined, s: undefined, b: undefined, d: undefined};
+		assert.deepStrictEqual(res, [empty, empty]);
+	});
+
+	it('E) CONVERT with a style keeps NULL as undefined', function () {
+		const res = alasql('SELECT CONVERT(STRING, a, 103) AS d FROM ?', [[{a: null}]]);
+		assert.deepStrictEqual(res, [{d: undefined}]);
+	});
+
+	it('F) Aggregates ignore NULL values after CAST', function () {
+		const res = alasql(
+			`SELECT AVG(CAST(a AS NUMBER)) AS av, SUM(CAST(a AS NUMBER)) AS s,
+				COUNT(CAST(a AS NUMBER)) AS c FROM ?`,
+			[[{a: null}, {a: 4}, {}]]
+		);
+		assert.deepStrictEqual(res, [{av: 4, s: 4, c: 1}]);
+	});
+
+	it('G) Non-null values are still converted', function () {
+		const res = alasql(
+			`SELECT CAST(a AS INT) AS i, CAST(a AS NUMBER) AS n, CAST(a AS STRING) AS s,
+				CAST(0 AS BOOLEAN) AS b FROM ?`,
+			[[{a: '12.7'}]]
+		);
+		assert.deepStrictEqual(res, [{i: 12, n: 12.7, s: '12.7', b: false}]);
+	});
+});