I do have to agree, although its certainly not the worst code block i have ever seen, it certainly could do with a bit of a tidy up.

Why if you are using a class that has PHP5 style syntax have you used 'var' instead of the visibility modifiers, if you want the class to be PHP4 compliant, you will need to remove your construct and replace it with the C++ style constructor (a method with the same name as the class), if not then use either 'public', 'private' or 'protected' instead of var (it used to call a E_STRICT warning, but i cant seem to replicate it).

Dont call non-static methods as static:
you call them using $this (unless declared as static, which isn't the case here):

PHP Code:

$this->co(); 


You need to also name your methods so that they are descriptive, I.E.

PHP Code:

public function connect() {}
public function disconnect() {}
public function execQuery() {} 


as opposed to:

PHP Code:

public function co() {}
public function cl() {}
public function q() {} 


Looking at the first example, i am immediately able to see what the method does because the name describes it well, therefore i don't need to actually read the code to find out what it does.

Apart from that its all personal preference. I personally would have the code block delimiters {} on a new line and I wouldn't use the bash comment style.

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mysql> SELECT * FROM `users` WHERE `users`.`clue` > 0;
Empty set (0.00 sec)