In SQL, wildcard characters can be used in "LIKE" expressions; the percent sign (%) matches zero or more characters, and underscore (_) a single character. Sometimes users are not familiar with these or they are using different ones like (*) and (+) similar to regular expressions. My colleages do so and then i decided to add this feature by extending CbCriteria. Especially adding a new parameter $wildcard_chars to the method addSearchCondition to replace them if needed with standard SQL characters:

class MyCDbCriteria extends CDbCriteria
{
/*
.....
*/  
public function addSearchCondition($column,$keyword,$escape=true,$operator='AND',$like='LIKE',$wildcard_chars = array('%'=>'%','_'=>'_'))
	{
    if($keyword=='') return $this;
    if($escape) 
    {
      $keyword='%'.strtr($keyword,array('%'=>'\%','_'=>'\_','\\'=>'\\\\')).'%';
    }
    else
    {
      $keyword=preg_replace(array("/".quotemeta($wildcard_chars['%'])."/","/".quotemeta($wildcard_chars['_'])."/"),array("%","_"),$keyword);
    }
    $condition=$column." $like ".self::PARAM_PREFIX.self::$paramCount;
    $this->params[self::PARAM_PREFIX.self::$paramCount++]=$keyword;
    return $this->addCondition($condition,$operator);
  }
/*
.....
*/
}    

Therfore of course it is necessary to overwrite the method compare too:

public function compare($column, $value, $partialMatch=false, $operator='AND', $escape=true,$wildcard_chars = array('%'=>'%','_'=>'_'))
	{
		if(is_array($value))
		{
			if($value===array())
				return $this;
			return $this->addInCondition($column,$value,$operator);
		}
		else
			$value="$value";

		if(preg_match('/^(?:\s*(<>|<=|>=|<|>|=))?(.*)$/',$value,$matches))
		{
			$value=$matches[2];
			$op=$matches[1];
		}
		else
			$op='';

		if($value==='')
			return $this;

		if($partialMatch)
		{
			if($op==='')
				return $this->addSearchCondition($column,$value,$escape,$operator,'LIKE',$wildcard_chars);
			if($op==='<>')
				return $this->addSearchCondition($column,$value,$escape,$operator,'NOT LIKE',$wildcard_chars);
		}
		else if($op==='')
			$op='=';

		$this->addCondition($column.$op.self::PARAM_PREFIX.self::$paramCount,$operator);
		$this->params[self::PARAM_PREFIX.self::$paramCount++]=$value;

		return $this;
	}

Now I can use my own very specail characters like '?' for any instead of '%'! This was my first article and i hope someone finds it useful.