Google-sheets – Had a query that worked but now doesn’t

The fix I used for this issue was to coerce the strings into a number by using ARRAYFORMULA(A1:A+0) in a new column adjacent to the original query (let's say column B).

I then used another query on the resulting data set and was able to sum(B) and avg(B) and format them as percentages successfully, as the type of column B was recognized as numeric.

the query only grabs the headers.

No, it grabs some rows, too. Scroll down... way, way down. There they are. Here's why you are hitting this.

1. Some of your columns are completely empty. These are interpreted as string by default. Hence, is not null is always true for these, and you get the whole table.
2. Since you order by B (ascending by default), the huge number of empty rows ends up on top, and leads you to conclude that the query returns nothing.

Unfortunately, there seem to be no way to declare the type of an empty column. This, combined with the "no nulls in string column" behavior, leads to people being driven crazy by not null.

To keep your sanity, either

• make sure every column has at least one nonempty cell, with some value of the type you expect in that column.
• or, use the less powerful but more straightforward filter command when it suffices for the task. Note that the output of filter can be fed into a query, to combine the best features of both.