GdaQueryFieldValue Represents a single value (or a parameter) The value held in this object can be of any type (a #GdaDictType object must be provided when creating the object). If the value can be considered as a parameter, then the possible values for this parameter can be limited by the result of the execution of a sub query (use the "value_provider*" properties to tell from which query field the values will be taken). @query: @type: @Returns: @field: @val: @field: @Returns: @field: @default_val: @field: @Returns: @field: @Returns: @field: @is_param: @field: @Returns: @field: @not_null: @field: @Returns: @field: @context: @Returns: @field: @model: @col: @error: @Returns: @field: @type: @field: @Returns: