Unsuccessful ZIP code join with weather data csv

[MSherwood1]

I have a weather data set for 50 zip codes and I am trying to join to a zipcode polygon shp (I have tried TIGER and the Living Atlas feature in PRO). It does the join but all the weather data fields are Null. I have made sure the field name for the Zip fields are identical. 

[DanPatterson · Accepted solution]

It isn't the field names that is important, it is the contents of the fields.  You can join text to text, number to number, but the contents must match.  For text, the case is important as well.  For numbers, don't be fooled by left justified "numbers" they have probably been converted to their text representation.

Also, if there is no data for a particular match, the row will contain an empty (null) value