public Select::addExpression($expression, $alias = NULL, $arguments = array())
Adds an expression to the list of "fields" to be SELECTed.
An expression can be any arbitrary string that is valid SQL. That includes various functions, which may in some cases be database-dependent. This method makes no effort to correct for database-specific functions.
Parameters
$expression: The expression string. May contain placeholders.
$alias: The alias for this expression. If not specified, one will be gener