Fix for Issue 2158 (AverageIf Calculation Problem)

Issue PHPOffice#2158 reports an error calculating AverageIf because a function returns null rather than a string. There turn out to be several components to this problem:
- The nominal fix to the problem is to add some null-to-nullstring coercion in DatabaseAbstract.
- This fixes the error, but does not necessarily lead to the correct result because buildQuery treats values of null and null-string identically, whereas Excel does not. So change that to treat null-string as any other string.
- But that doesn't lead to the correct result either. That's because Functions/ifCondition recognizes a null string, but then continues to (over-)process it until it returns the wrong result. Fix this problem in conjunction with the other two, and we finally get the correct result.

A new unit test is added for AVERAGEIF, and new test cases are added for SUMIF. In each case, there are complementary tests for conditions of null and null-string, and the results agree with Excel. There may or may not be value in adding new tests to other functions, and I will be glad to do so for any functions which you care to identify, but no existing tests broke as a result of these changes.

src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php

@@ -95,7 +95,7 @@ private static function buildQuery(array $criteriaNames, array $criteria): strin
         foreach ($criteria as $key => $criterion) {
             foreach ($criterion as $field => $value) {
                 $criterionName = $criteriaNames[$field];
-                if ($value !== null && $value !== '') {
+                if ($value !== null) {
                     $condition = self::buildCondition($value, $criterionName);
                     $baseQuery[$key][] = $condition;
                 }
@@ -104,12 +104,12 @@ private static function buildQuery(array $criteriaNames, array $criteria): strin
 
         $rowQuery = array_map(
             function ($rowValue) {
-                return (count($rowValue) > 1) ? 'AND(' . implode(',', $rowValue) . ')' : $rowValue[0];
+                return (count($rowValue) > 1) ? 'AND(' . implode(',', $rowValue) . ')' : ($rowValue[0] ?? '');
             },
             $baseQuery
         );
 
-        return (count($rowQuery) > 1) ? 'OR(' . implode(',', $rowQuery) . ')' : $rowQuery[0];
+        return (count($rowQuery) > 1) ? 'OR(' . implode(',', $rowQuery) . ')' : ($rowQuery[0] ?? '');
     }
 
     private static function buildCondition($criterion, string $criterionName): string

src/PhpSpreadsheet/Calculation/Functions.php

@@ -251,7 +251,7 @@ public static function ifCondition($condition)
         $condition = self::flattenSingleValue($condition);
 
         if ($condition === '') {
-            $condition = '=""';
+            return '=""';
         }
         if (!is_string($condition) || !in_array($condition[0], ['>', '<', '='])) {
             $condition = self::operandSpecialHandling($condition);

tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfTest.php

@@ -20,8 +20,7 @@ public function testSUMIF2($expectedResult, array $array1, $condition, ?array $a
         $sheet->fromArray($array1, null, 'A1', true);
         $maxARow = count($array1);
         $firstArg = "A1:A$maxARow";
-        //$secondArg = is_string($condition) ? "\"$condition\"" : $condition;
-        $sheet->getCell('B1')->setValue($condition);
+        $this->setCell('B1', $condition);
         $secondArg = 'B1';
         if (empty($array2)) {
             $sheet->getCell('D1')->setValue("=SUMIF($firstArg, $secondArg)");

tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIf2Test.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PHPUnit\Framework\TestCase;
+
+class AverageIf2Test extends TestCase
+{
+    public function testAVERAGEIF(): void
+    {
+        $table = [
+            ['n', 1],
+            ['', 2],
+            ['y', 3],
+            ['', 4],
+            ['n', 5],
+            ['n', 6],
+            ['n', 7],
+            ['', 8],
+            [null, 9],
+        ];
+
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $sheet->fromArray($table, null, 'A1', true);
+        $sheet->getCell('C1')->setValue('=AVERAGEIF(A:A,"",B:B)');
+        $sheet->getCell('C2')->setValue('=AVERAGEIF(A:A,,B:B)');
+        $sheet->getCell('C3')->setValue('=AVERAGEIF(A:A,"n",B:B)');
+        $sheet->getCell('C4')->setValue('=AVERAGEIF(A:A,"y",B:B)');
+        $sheet->getCell('C5')->setValue('=AVERAGEIF(A:A,"x",B:B)');
+
+        self::assertEqualsWithDelta(5.75, $sheet->getCell('C1')->getCalculatedValue(), 1E-12);
+        self::assertEquals('#DIV/0!', $sheet->getCell('C2')->getCalculatedValue());
+        self::assertEqualsWithDelta(4.75, $sheet->getCell('C3')->getCalculatedValue(), 1E-12);
+        self::assertEqualsWithDelta(3, $sheet->getCell('C4')->getCalculatedValue(), 1E-12);
+        self::assertEquals('#DIV/0!', $sheet->getCell('C5')->getCalculatedValue());
+        $spreadsheet->disconnectWorksheets();
+    }
+}

tests/data/Calculation/MathTrig/SUMIF.php

@@ -150,4 +150,22 @@
         'North ?',
         [[36693], [22100], ['=3/0'], [34440], [29889], [50090], [32080], [45500]],
     ],
+    [
+        23,
+        [['n'], [''], ['y'], [''], ['n'], ['n'], ['n'], [''], []],
+        '',
+        [[1], [2], [3], [4], [5], [6], [7], [8], [9]],
+    ],
+    [
+        0,
+        [['n'], [''], ['y'], [''], ['n'], ['n'], ['n'], [''], []],
+        null,
+        [[1], [2], [3], [4], [5], [6], [7], [8], [9]],
+    ],
+    [
+        19,
+        [['n'], [''], ['y'], [''], ['n'], ['n'], ['n'], [''], []],
+        'n',
+        [[1], [2], [3], [4], [5], [6], [7], [8], [9]],
+    ],
 ];