Loop over JDBC request until assertation is Valid

Groovy is good pair to SoapUI. Of course, javascript is supported.

I believe, you should be able to use for loop in javascript too, have you check in the internet for the same?

Something like below:
https://www.w3schools.com/js/js_loop_for.asp

for (i = 0; i < cars.length; i++) {
text += cars[i] + "<br>";
}

Similarly wait function
http://stackoverflow.com/questions/15694470/javascript-wait-function