Add subquery support for "from" and "table"

src/Illuminate/Database/Capsule/Manager.php

@@ -77,13 +77,14 @@ public static function connection($connection = null)
     /**
      * Get a fluent query builder instance.
      *
-     * @param  string  $table
+     * @param  \Closure|\Illuminate\Database\Query\Builder|string  $table
+     * @param  string|null  $as
      * @param  string|null  $connection
      * @return \Illuminate\Database\Query\Builder
      */
-    public static function table($table, $connection = null)
+    public static function table($table, $as = null, $connection = null)
     {
-        return static::$instance->connection($connection)->table($table);
+        return static::$instance->connection($connection)->table($table, $as);
     }
 
     /**

src/Illuminate/Database/Connection.php

@@ -257,12 +257,13 @@ public function getSchemaBuilder()
     /**
      * Begin a fluent query against a database table.
      *
-     * @param  string  $table
+     * @param  \Closure|\Illuminate\Database\Query\Builder|string  $table
+     * @param  string|null  $as
      * @return \Illuminate\Database\Query\Builder
      */
-    public function table($table)
+    public function table($table, $as = null)
     {
-        return $this->query()->from($table);
+        return $this->query()->from($table, $as);
     }
 
     /**

src/Illuminate/Database/ConnectionInterface.php

@@ -9,10 +9,11 @@ interface ConnectionInterface
     /**
      * Begin a fluent query against a database table.
      *
-     * @param  string  $table
+     * @param  \Closure|\Illuminate\Database\Query\Builder|string  $table
+     * @param  string|null  $as
      * @return \Illuminate\Database\Query\Builder
      */
-    public function table($table);
+    public function table($table, $as = null);
 
     /**
      * Get a new raw query expression.

src/Illuminate/Database/Query/Builder.php

@@ -367,12 +367,19 @@ public function distinct()
     /**
      * Set the table which the query is targeting.
      *
-     * @param  string  $table
+     * @param  \Closure|\Illuminate\Database\Query\Builder|string  $table
+     * @param  string|null  $as
      * @return $this
      */
-    public function from($table)
+    public function from($table, $as = null)
     {
-        $this->from = $table;
+        if ($table instanceof self ||
+            $table instanceof EloquentBuilder ||
+            $table instanceof Closure) {
+            return $this->fromSub($table, $as);
+        }
+
+        $this->from = $as ? "{$table} as {$as}" : $table;
 
         return $this;
     }

tests/Integration/Database/QueryBuilderTest.php

@@ -31,6 +31,21 @@ protected function setUp(): void
         ]);
     }
 
+    public function testFromWithAlias()
+    {
+        $this->assertSame('select * from "posts" as "alias"', DB::table('posts', 'alias')->toSql());
+    }
+
+    public function testFromWithSubQuery()
+    {
+        $this->assertSame(
+            'Fake Post',
+            DB::table(function ($query) {
+                $query->selectRaw("'Fake Post' as title");
+            }, 'posts')->first()->title
+        );
+    }
+
     public function testWhereDate()
     {
         $this->assertSame(1, DB::table('posts')->whereDate('created_at', '2018-01-02')->count());