public Update::expression($field, $expression, array $arguments = NULL)
Specifies fields to be updated as an expression.
Expression fields are cases such as counter=counter+1. This method takes precedence over fields().
Parameters
$field: The field to set.
$expression: The field will be set to the value of this expression. This parameter may include named placeholders.
$arguments: If specified, this is an array of key/value pairs for named placeholders corresponding to the expression.
Return v