Revert/optimize some changes from 48a2baf0e288accd206f5da5031d29076e130792
diff --git a/system/database/drivers/cubrid/cubrid_driver.php b/system/database/drivers/cubrid/cubrid_driver.php
index b7763d9..971f1ea 100644
--- a/system/database/drivers/cubrid/cubrid_driver.php
+++ b/system/database/drivers/cubrid/cubrid_driver.php
@@ -74,7 +74,7 @@
 		else
 		{
 			// If no port is defined by the user, use the default value
-			$this->port === '' OR $this->port = 33000;
+			empty($this->port) OR $this->port = 33000;
 		}
 	}
 
diff --git a/system/database/drivers/mssql/mssql_driver.php b/system/database/drivers/mssql/mssql_driver.php
index 5bd6669..697b2fd 100644
--- a/system/database/drivers/mssql/mssql_driver.php
+++ b/system/database/drivers/mssql/mssql_driver.php
@@ -64,7 +64,7 @@
 	 */
 	public function db_connect()
 	{
-		if ($this->port !== '')
+		if ( ! empty($this->port))
 		{
 			$this->hostname .= ','.$this->port;
 		}
@@ -81,7 +81,7 @@
 	 */
 	public function db_pconnect()
 	{
-		if ($this->port !== '')
+		if ( ! empty($this->port))
 		{
 			$this->hostname .= ','.$this->port;
 		}
diff --git a/system/database/drivers/mysql/mysql_driver.php b/system/database/drivers/mysql/mysql_driver.php
index fc9bbdc..5937b22 100644
--- a/system/database/drivers/mysql/mysql_driver.php
+++ b/system/database/drivers/mysql/mysql_driver.php
@@ -68,7 +68,7 @@
 	{
 		parent::__construct($params);
 
-		if ($this->port !== '')
+		if ( ! empty($this->port))
 		{
 			$this->hostname .= ':'.$this->port;
 		}
diff --git a/system/database/drivers/mysqli/mysqli_driver.php b/system/database/drivers/mysqli/mysqli_driver.php
index 5814ace..02f8937 100644
--- a/system/database/drivers/mysqli/mysqli_driver.php
+++ b/system/database/drivers/mysqli/mysqli_driver.php
@@ -71,9 +71,9 @@
 	 */
 	public function db_connect()
 	{
-		return ($this->port !== '')
-			? @new mysqli($this->hostname, $this->username, $this->password, $this->database, $this->port)
-			: @new mysqli($this->hostname, $this->username, $this->password, $this->database);
+		return empty($this->port)
+			? @new mysqli($this->hostname, $this->username, $this->password, $this->database)
+			: @new mysqli($this->hostname, $this->username, $this->password, $this->database, $this->port);
 	}
 
 	// --------------------------------------------------------------------
@@ -91,9 +91,9 @@
 			return $this->db_connect();
 		}
 
-		return ($this->port !== '')
-			? @new mysqli('p:'.$this->hostname, $this->username, $this->password, $this->database, $this->port)
-			: @new mysqli('p:'.$this->hostname, $this->username, $this->password, $this->database);
+		return empty($this->port)
+			? @new mysqli('p:'.$this->hostname, $this->username, $this->password, $this->database)
+			: @new mysqli('p:'.$this->hostname, $this->username, $this->password, $this->database, $this->port);
 	}
 
 	// --------------------------------------------------------------------
diff --git a/system/database/drivers/odbc/odbc_driver.php b/system/database/drivers/odbc/odbc_driver.php
index b493e93..c3735da 100644
--- a/system/database/drivers/odbc/odbc_driver.php
+++ b/system/database/drivers/odbc/odbc_driver.php
@@ -64,7 +64,7 @@
 		$this->_random_keyword = ' RND('.time().')'; // database specific random keyword
 
 		// Legacy support for DSN in the hostname field
-		if ($this->dsn === '')
+		if (empty($this->dsn))
 		{
 			$this->dsn = $this->hostname;
 		}
@@ -254,9 +254,9 @@
 	 */
 	protected function _list_tables($prefix_limit = FALSE)
 	{
-		$sql = "SHOW TABLES FROM `".$this->database."`";
+		$sql = 'SHOW TABLES FROM '.$this->database;
 
-		if ($prefix_limit !== FALSE AND $this->dbprefix !== '')
+		if ($prefix_limit !== FALSE && $this->dbprefix !== '')
 		{
 			//$sql .= " LIKE '".$this->escape_like_str($this->dbprefix)."%' ".sprintf($this->_like_escape_str, $this->_like_escape_chr);
 			return FALSE; // not currently supported
diff --git a/system/database/drivers/sqlite/sqlite_driver.php b/system/database/drivers/sqlite/sqlite_driver.php
index c87a16b..d9820e1 100644
--- a/system/database/drivers/sqlite/sqlite_driver.php
+++ b/system/database/drivers/sqlite/sqlite_driver.php
@@ -279,7 +279,7 @@
 	{
 		$sql = "SELECT name from sqlite_master WHERE type='table'";
 
-		if ($prefix_limit !== FALSE AND $this->dbprefix != '')
+		if ($prefix_limit !== FALSE && $this->dbprefix != '')
 		{
 			$sql .= " AND 'name' LIKE '".$this->escape_like_str($this->dbprefix)."%' ".sprintf($this->_like_escape_str, $this->_like_escape_chr);
 		}