I will answer, as I understand.
Let's admit, you have in request five fields with parameters.
If the parameter is passed - that it does not mean that Aks ceases to pay to it attention, the type - well is not present, so is not present. Simply this parameter accepts value "", that is - empty value. Accordingly, the request will search for a line with coincidence on the sample of the gated in parameters and with two or how many there empty field values from "passed". And if such coincidence it is not found - you receive the blank line.
Now on your second question.
The request with parameter as it is - not so convenient piece as you were convinced. As the variant - to be played with variables, but it is not always convenient.
It is possible to make easier. Make the form, make on it empty fields with the necessary formatting. Also make the same request which as parameters will take values from form fields.
It can directly be necessary in request to transform value of this or that field of the form to the necessary data type.
It is in certain cases convenient to make the table with fields of the necessary data types, and it to fasten to the form on which values will be hammered into query parameters.
It can be necessary to make a series of serial requests, correctly to fulfill all variants of values, including with empty fields.