Sort nulls consistently

PostgreSQL normally sorts nulls after everything else in ascending order
and vice versa; we reverse this, to match SQLIte and MySQL

lib/Db/Driver.php

@@ -75,6 +75,8 @@ interface Driver {
      * - "nocase": the name of a general-purpose case-insensitive collation sequence
      * - "like": the case-insensitive LIKE operator
      * - "integer": the integer type to use for explicit casts
+     * - "asc": ascending sort order
+     * - "desc": descending sort order
      */
     public function sqlToken(string $token): string;
 

lib/Db/MySQL/Driver.php

@@ -83,6 +83,8 @@ class Driver extends \JKingWeb\Arsse\Db\AbstractDriver {
                 return '"utf8mb4_unicode_ci"';
             case "integer":
                 return "signed integer";
+            case "asc":
+                return "";
             default:
                 return $token;
         }

lib/Db/PostgreSQL/Driver.php

@@ -119,6 +119,10 @@ class Driver extends \JKingWeb\Arsse\Db\AbstractDriver {
                 return '"und-x-icu"';
             case "like":
                 return "ilike";
+            case "asc":
+                return "nulls first";
+            case "desc":
+                return "desc nulls last";
             default:
                 return $token;
         }

lib/Db/SQLite3/Driver.php

@@ -114,6 +114,8 @@ class Driver extends \JKingWeb\Arsse\Db\AbstractDriver {
         switch (strtolower($token)) {
             case "greatest":
                 return "max";
+            case "asc":
+                return "";
             default:
                 return $token;
         }

tests/cases/Db/BaseDriver.php

@@ -385,6 +385,8 @@ abstract class BaseDriver extends \JKingWeb\Arsse\Test\AbstractTest {
         $nocase = $this->drv->sqlToken("noCASE");
         $like = $this->drv->sqlToken("liKe");
         $integer = $this->drv->sqlToken("InTEGer");
+        $asc = $this->drv->sqlToken("asc");
+        $desc = $this->drv->sqlToken("desc");
 
         $this->assertSame("NOT_A_TOKEN", $this->drv->sqlToken("NOT_A_TOKEN"));
 
@@ -392,5 +394,7 @@ abstract class BaseDriver extends \JKingWeb\Arsse\Test\AbstractTest {
         $this->assertSame("Z", $this->drv->query("SELECT 'Z' collate $nocase")->getValue());
         $this->assertSame("Z", $this->drv->query("SELECT 'Z' where 'Z' $like 'z'")->getValue());
         $this->assertEquals(1, $this->drv->query("SELECT CAST((1=1) as $integer)")->getValue());
+        $this->assertEquals([null, 1], array_column($this->drv->query("SELECT 1 as t union select null as t order by t $asc")->getAll(), "t"));
+        $this->assertEquals([1, null], array_column($this->drv->query("SELECT 1 as t union select null as t order by t $desc")->getAll(), "t"));
     }
 }