Spalten tauschen in PostgreSQL

Das Vertauschen von SQL-Tabellenspalten gehört bei MySQL zum Standardrepertoire – bei PostgreSQL wird dies (noch) nicht unterstützt. Zwar widmet das offizielle Wiki dem Problem einen eigenen Beitrag, zeigt aber keine praktikable Lösung auf, die auch Views, Indizes und Triggers unterstützt. Folgende Klasse erledigt diesen Job (sowohl für MySQL als auch für PostgreSQL) entweder auf der Kommandozeile – oder alternativ direkt in Laravel 5.


<?php
namespace App\Helpers;
class ColumnChanger
{

	public static $quotes;

	public static $path;

	public static function swap($table, $col1, $col2)
	{

		// initialize

		self::$quotes = self::getQuotes();
		self::$path = self::getPath();

		// export

		$content = self::exportDB();

		// swap

		$content = self::swapNow($table, $col1, $col2, $content);

		// import

		self::importDB($content);
	}

	public static function getQuotes()
	{
		if (getenv("DB_CONNECTION") == "pgsql")
		{
			return "";
		}

		if (getenv("DB_CONNECTION") == "mysql")
		{
			return "`";
		}
	}

	public static function getPath()
	{
		if (getenv("DB_CONNECTION") == "pgsql")
		{
			$sql = new \PDO('pgsql:host=' . getenv('DB_HOST') . ';port=' . getenv('DB_PORT') . ';dbname=' . getenv('DB_DATABASE') , getenv('DB_USERNAME') , getenv('DB_PASSWORD'));
			$stmt = $sql->prepare("SHOW data_directory");
			$stmt->execute();
			$path = str_replace("data", "bin", $stmt->fetchObject()->data_directory) . "/";
		}

		if (getenv("DB_CONNECTION") == "mysql")
		{
			$sql = new \PDO('mysql:host=' . getenv('DB_HOST') . ';port=' . getenv('DB_PORT') . ';dbname=' . getenv('DB_DATABASE') , getenv('DB_USERNAME') , getenv('DB_PASSWORD'));
			$stmt = $sql->prepare("SHOW VARIABLES LIKE 'basedir'");
			$stmt->execute();
			$path = $stmt->fetchObject()->Value . "bin/";
		}

		return $path;
	}

	public static function exportDB()
	{
		if (getenv("DB_CONNECTION") == "pgsql")
		{
			putenv("PGPASSWORD=" . getenv('DB_PASSWORD'));
			exec('"' . self::$path . 'pg_dump" --clean --inserts -h ' . getenv('DB_HOST') . ' -p ' . getenv('DB_PORT') . ' -U ' . getenv('DB_USERNAME') . ' ' . getenv('DB_DATABASE') . ' > db.sql');
		}

		if (getenv("DB_CONNECTION") == "mysql")
		{
			exec('"' . self::$path . 'mysqldump" -h ' . getenv('DB_HOST') . ' --port ' . getenv('DB_PORT') . ' -u ' . getenv('DB_USERNAME') . ' -p"' . getenv('DB_PASSWORD') . '" ' . getenv('DB_DATABASE') . ' > db.sql');
		}

		return file_get_contents("db.sql");
	}

	public static function importDB($content)
	{
		file_put_contents("db.sql", $content);
		if (getenv("DB_CONNECTION") == "pgsql")
		{
			putenv("PGPASSWORD=" . getenv('DB_PASSWORD'));
			exec('"' . self::$path . 'psql" -h ' . getenv('DB_HOST') . ' -p ' . getenv('DB_PORT') . ' -U ' . getenv('DB_USERNAME') . ' -d ' . getenv('DB_DATABASE') . ' -1 -f db.sql');
		}

		if (getenv("DB_CONNECTION") == "mysql")
		{
			exec('"' . self::$path . 'mysql" -h ' . getenv('DB_HOST') . ' --port ' . getenv('DB_PORT') . ' -u ' . getenv('DB_USERNAME') . ' -p"' . getenv('DB_PASSWORD') . '" ' . getenv('DB_DATABASE') . ' --default-character-set=utf8 < db.sql');
		}

		unlink("db.sql");
	}

	public static function getPositions($haystack, $needle)
	{
		$positions = [];
		$lastPos = 0;
		while (($lastPos = strpos($haystack, $needle, $lastPos)) !== false)
		{
			$positions[] = $lastPos;
			$lastPos = $lastPos + strlen($needle);
		}

		return $positions;
	}

	public static function getEnd($content, $begin)
	{
		$end = $begin;
		$outside = true;
		while ($outside !== true || $content[$end] != ";")
		{
			if ($content[$end] == "'")
			{
				if ($end === 0 || $content[$end - 1] != "\")
				{
					$outside = !$outside;
				}
			}

			$end++;
		}

		return ++$end;
	}

	public static function splitString($string)
	{
		return preg_split('/(?<!^)(?!$)/u', $string);
	}

	public static function getColumns($query)
	{
		$i = 0;
		$outside = true;
		$query = self::splitString($query);
		foreach($query as $i => $char)
		{
			if ($query[$i] == "'")
			{
				if ($i === 0 || $query[$i - 1] != "\")
				{
					$outside = !$outside;
				}
			}

			if ($outside === true && $query[$i] == ",")
			{
				$query[$i] = "♥";
			}

			$i++;
		}

		$query = implode("", $query);
		$cols = explode("♥", $query);
		return $cols;
	}

	public static function swapNow($table, $col1, $col2, $content)
	{

		// loop through relevant statements

		foreach(["CREATE TABLE " . self::$quotes . $table . self::$quotes, "INSERT INTO " . self::$quotes . $table . self::$quotes] as $skey => $statement)
		{
			$positions = self::getPositions($content, $statement);
			foreach($positions as $position)
			{
				$begin = $position;
				$end = self::getEnd($content, $begin);
				$query_all = substr($content, $begin, $end - $begin);
				$query_inside = substr($query_all, strpos($query_all, "(") + 1, strrpos($query_all, ")") - strpos($query_all, "(") - 1);

				// get columns

				$cols = self::getColumns($query_inside);

				// get relevant column indexes

				if ($skey == 0)
				{
					$col1pos = 0;
					$col2pos = 0;
					foreach($cols as $pos => $col)
					{
						$col = trim($col);
						if (strpos($col, self::$quotes . $col1 . self::$quotes) === 0)
						{
							$col1pos = $pos;
						}

						if (strpos($col, self::$quotes . $col2 . self::$quotes) === 0)
						{
							$col2pos = $pos;
						}
					}
				}

				// swap columns

				$tmp = $cols[$col1pos];
				$cols[$col1pos] = $cols[$col2pos];
				$cols[$col2pos] = $tmp;
				$query_inside_new = implode(",", $cols);

				// insert query into content

				$query_all_new = str_replace($query_inside, $query_inside_new, $query_all);
				$content = str_replace($query_all, $query_all_new, $content);
			}
		}

		return $content;
	}
}

// usage from the command line

if (isset($argv) && is_array($argv))
{
	$args = [];
	foreach($argv as $key => $arg)
	{
		switch ($arg)
		{
		case "-e":
			$args["engine"] = $argv[$key + 1];
			break;

		case "-h":
			$args["hostname"] = $argv[$key + 1];
			break;

		case "-P":
			$args["port"] = $argv[$key + 1];
			break;

		case "-u":
			$args["username"] = $argv[$key + 1];
			break;

		case "-p":
			$args["password"] = $argv[$key + 1];
			break;

		case "-d":
			$args["database"] = $argv[$key + 1];
			break;

		case "-t":
			$args["table"] = $argv[$key + 1];
			break;
		}
	}

	// set default values

	if (!isset($args["hostname"]))
	{
		$args["hostname"] = "127.0.0.1";
	}

	if (!isset($args["port"]) && isset($args["engine"]) && $args["engine"] == "mysql")
	{
		$args["port"] = "3306";
	}

	if (!isset($args["port"]) && isset($args["engine"]) && $args["engine"] == "pgsql")
	{
		$args["port"] = "5432";
	}

	foreach($args as $option => $arg)
	{
		if (!isset($arg))
		{
			die('missing option ' . $option);
		}
	}

	if (count($argv) < 2)
	{
		die('error');
	}

	$args["col1"] = $argv[count($argv) - 2];
	$args["col2"] = $argv[count($argv) - 1];
	putenv("DB_CONNECTION=" . $args["engine"]);
	putenv("DB_HOST=" . $args["hostname"]);
	putenv("DB_PORT=" . $args["port"]);
	putenv("DB_DATABASE=" . $args["database"]);
	putenv("DB_USERNAME=" . $args["username"]);
	putenv("DB_PASSWORD=" . $args["password"]);
	ColumnChanger::swap($args["table"], $args["col1"], $args["col2"]);
	
}

Der Aufruf auf der Kommandozeile ist selbsterklärend:

php ColumnChanger.php -e pgsql -h 127.0.0.1 -P 5432 -u username -p password -d database -t table col1 col2
php ColumnChanger.php -e mysql -h 127.0.0.1 -P 3306 -u username -p password -d database -t table col1 col2

Auch die Integration in Laravel 5 ist durch einfaches Kopieren von ColumnChanger.php in den Ordner app/Helpers schnell erledigt. Innerhalb von Migrations kann man dann direkt Spalten vertauschen:

<?php
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class SwitchColumns extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        App\Helpers\ColumnChanger::swap("users","email","password");
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        App\Helpers\ColumnChanger::swap("users","password","email");
    }
}
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