使用if在循环中检查mysql_fetch_array中的列

I'm a novice at PHP to do MySQL manipulations. When the problem is boiled down, the database has 2 columns - city, borough. Some cities have a borough and the field is populated. Some cities do not, and the borough field is null. I only want to retrieve data into an array if the borough field is populated. My code looks like:I'm a novice at PHP to do MySQL manipulations.