Added a way to retrieve the first column of the first row from a query. (#41858)

* Added a way to retrieve the first column of the first row from a query result.

* styleci fixes

Author: peterlupu

src/Illuminate/Database/Connection.php

@@ -334,6 +334,33 @@ public function selectOne($query, $bindings = [], $useReadPdo = true)
         return array_shift($records);
     }
 
+    /**
+     * Run a select statement and return the first column of the first row.
+     *
+     * @param  string  $query
+     * @param  array  $bindings
+     * @param  bool  $useReadPdo
+     * @return mixed
+     *
+     * @throws MultipleColumnsSelectedException
+     */
+    public function scalar($query, $bindings = [], $useReadPdo = true)
+    {
+        $record = $this->selectOne($query, $bindings, $useReadPdo);
+
+        if (is_null($record)) {
+            return null;
+        }
+
+        $record = (array) $record;
+
+        if (count($record) > 1) {
+            throw new MultipleColumnsSelectedException;
+        }
+
+        return reset($record);
+    }
+
     /**
      * Run a select statement against the database.
      *

src/Illuminate/Database/MultipleColumnsSelectedException.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Illuminate\Database;
+
+use RuntimeException;
+
+class MultipleColumnsSelectedException extends RuntimeException
+{
+    //
+}

tests/Database/DatabaseConnectionTest.php

@@ -11,6 +11,7 @@
 use Illuminate\Database\Events\TransactionBeginning;
 use Illuminate\Database\Events\TransactionCommitted;
 use Illuminate\Database\Events\TransactionRolledBack;
+use Illuminate\Database\MultipleColumnsSelectedException;
 use Illuminate\Database\Query\Builder as BaseBuilder;
 use Illuminate\Database\Query\Grammars\Grammar;
 use Illuminate\Database\Query\Processors\Processor;
@@ -56,6 +57,28 @@ public function testSelectOneCallsSelectAndReturnsSingleResult()
         $this->assertSame('foo', $connection->selectOne('foo', ['bar' => 'baz']));
     }
 
+    public function testScalarCallsSelectOneAndReturnsSingleResult()
+    {
+        $connection = $this->getMockConnection(['selectOne']);
+        $connection->expects($this->once())->method('selectOne')->with('select count(*) from tbl')->willReturn((object) ['count(*)' => 5]);
+        $this->assertSame(5, $connection->scalar('select count(*) from tbl'));
+    }
+
+    public function testScalarThrowsExceptionIfMultipleColumnsAreSelected()
+    {
+        $connection = $this->getMockConnection(['selectOne']);
+        $connection->expects($this->once())->method('selectOne')->with('select a, b from tbl')->willReturn((object) ['a' => 'a', 'b' => 'b']);
+        $this->expectException(MultipleColumnsSelectedException::class);
+        $connection->scalar('select a, b from tbl');
+    }
+
+    public function testScalarReturnsNullIfUnderlyingSelectReturnsNoRows()
+    {
+        $connection = $this->getMockConnection(['selectOne']);
+        $connection->expects($this->once())->method('selectOne')->with('select foo from tbl where 0=1')->willReturn(null);
+        $this->assertNull($connection->scalar('select foo from tbl where 0=1'));
+    }
+
     public function testSelectProperlyCallsPDO()
     {
         $pdo = $this->getMockBuilder(DatabaseConnectionTestMockPDO::class)->onlyMethods(['prepare'])->getMock();