Will users understand “* to 10”?

Question

To let users search by number or date, I want to provide two inputs. If you have two inputs, its a range search. If you have one input, it's a "greater than or equals" or "less than or equals". Will users understand they may leave one input blank? If not, how to make it discoverable?

values: 1 ,2, 3, 4, 5, 6, 7, 8, 9, 10

inputs: -- 5
meaning: "not greater than 5" 
result: 1, 2, 3, 4, 5

5 --
"not less than 5" 
5, 6, 7, 8, 9, 10

3 6
"not less than 3, not greater than 6"
3, 4, 5, 6

Answer 1

Symbols for not greater than and not less than are usually like this

• <= 5 - not greater than 5
• >= 3 - not smaller than 3
• 3 .. 5 - between 3 and 5

If you want to make clear that empty field means no max/min, you can:

• gray it out and/or
• add placeholder e.g. "Any"

^{download bmml source – Wireframes created with Balsamiq Mockups}

Or use min value/max value instead of "Any" if they are known to you.

Answer 2

I personally think you might be right and users might not understand that leaving an input blank means there is not minimum or maximum.

You could solve this by adding a placeholder.
Leave blank for no minimum
Leave blank for no maximum
The problem with placeholders is that users might forget about the hint as soon as the placeholder disappears.

A label might be a better solution.
Leave blank for no minimum or maximum

When the max number (and min) is known to you, you could also think about a range slider.

This example shows a range slider on a webshop. The cheapest product in the category is 12 euros. The most expensive is 850 euros.
This however, might not really work for dates.

A final, possible solution is something I've seen on a website listing houses for sale. It has maximum price ranges at different increments listed in a select box with the final option "No maximum". This works if you have a small range of numbers, but since your input can contain both numbers and dates, this might not work for you. This is a solution, slightly based on the concept:

^{download bmml source – Wireframes created with Balsamiq Mockups}

I hope this gives you some inspiration. There is no one, best solution I'm afraid.

Answer 3

If the value are fixed (1-10) I would suggest to use a number picker similar to date range pickers. See an example below:

Users should be able select a range by selecting a start and end number. Also, it would be nice to allow them to select not only range but any value even without range (see the 3rd example).