issue-36: add primary key for migration_table

src/Database/DblibDatabase.php

@@ -57,7 +57,7 @@ protected function createTableIfNotExists($database, $createTable)
     public function createVersion()
     {
         $database = preg_replace('~^/~', '', $this->getDbDriver()->getUri()->getPath());
-        $createTable = 'CREATE TABLE ' . $this->getMigrationTable() . ' (version int, status varchar(20))';
+        $createTable = 'CREATE TABLE ' . $this->getMigrationTable() . ' (version int, status varchar(20), PRIMARY KEY (version))';
         $this->createTableIfNotExists($database, $createTable);
         $this->checkExistsVersion();
     }

src/Database/MySqlDatabase.php

@@ -40,7 +40,7 @@ public function dropDatabase()
      */
     public function createVersion()
     {
-        $this->getDbDriver()->execute('CREATE TABLE IF NOT EXISTS ' . $this->getMigrationTable() . ' (version int, status varchar(20))');
+        $this->getDbDriver()->execute('CREATE TABLE IF NOT EXISTS ' . $this->getMigrationTable() . ' (version int, status varchar(20), PRIMARY KEY (version))');
         $this->checkExistsVersion();
     }
 

src/Database/PgsqlDatabase.php

@@ -60,7 +60,7 @@ public function dropDatabase()
      */
     public function createVersion()
     {
-        $this->getDbDriver()->execute('CREATE TABLE IF NOT EXISTS ' . $this->getMigrationTable() . ' (version int, status varchar(20))');
+        $this->getDbDriver()->execute('CREATE TABLE IF NOT EXISTS ' . $this->getMigrationTable() . ' (version int, status varchar(20), PRIMARY KEY (version))');
         $this->checkExistsVersion();
     }
 

src/Database/SqliteDatabase.php

@@ -36,7 +36,7 @@ public function dropDatabase()
      */
     public function createVersion()
     {
-        $this->getDbDriver()->execute('CREATE TABLE IF NOT EXISTS ' . $this->getMigrationTable() . ' (version int, status varchar(20))');
+        $this->getDbDriver()->execute('CREATE TABLE IF NOT EXISTS ' . $this->getMigrationTable() . ' (version int, status varchar(20), PRIMARY KEY (version))');
         $this->checkExistsVersion();
     }