core-bundle/src/Resources/contao/library/Contao/Database.php
public static function quoteIdentifier($strName)
	{
		static $strQuoteCharacter = null;

		if ($strQuoteCharacter === null)
		{
			$strQuoteCharacter = System::getContainer()->get('database_connection')->getDatabasePlatform()->getIdentifierQuoteCharacter();
		}

		// The identifier is quoted already
		if (strncmp($strName, $strQuoteCharacter, 1) === 0)
		{
			return $strName;
		}

		// Not an identifier (AbstractPlatform::quoteIdentifier() handles table.column so also allow . here)
		if (!preg_match('/^[A-Za-z0-9_$.]+$/', $strName))
		{
			return $strName;
		}

		return System::getContainer()->get('database_connection')->quoteIdentifier($strName);
	}
public static function quoteIdentifier($strName)
	{
		static $strQuoteCharacter = null;

		if ($strQuoteCharacter === null)
		{
			$strQuoteCharacter = System::getContainer()->get('database_connection')->getDatabasePlatform()->getIdentifierQuoteCharacter();
		}

		// The identifier is quoted already
		if (strncmp($strName, $strQuoteCharacter, 1) === 0)
		{
			return $strName;
		}

		// Not an identifier (AbstractPlatform::quoteIdentifier() handles table.column so also allow . here)
		if (!preg_match('/^[A-Za-z0-9_$.]+$/', $strName))
		{
			return $strName;
		}

		return System::getContainer()->get('database_connection')->quoteIdentifier($strName);
	}
Quote the column name if it is a reserved word

@param string $strName

@return string