INSERT OVERWRITE TABLE but change single field

I am looking to update a field for all items in a table if the value of the field is an empty string.

For context, I can get a count of the number of items that I need to update with this query:

select count(*) from ddb_table where someField = "";

I then want to update the items in this table where someField is an empty string. For example, I want to update someField to "foo" where the field is blank.

I imagine the INSERT OVERWRITE query would look something like this:

insert overwrite ddb_table select field1, field2, field3, field4, someField = "foo" FROM ddb_table where someField = "";

In other words, I'm wanting to "keep" all the original values for each item in the table, except for someField, which I want to update to "foo". This update would only occur on items where someField is blank.

How do I do this?

For my original query:

insert overwrite table ddb_table select field1, field2, field3, field4, someField = "foo" FROM ddb_table where someField = "";

The result was that someField appeared to take the value that was in field4, and field4 would get set to FALSE.

I then tried:

insert overwrite table ddb_table select field1, field2, field3, field4, "foo" as someField FROM ddb_table where someField = "";

This was slightly better, except that field4 would be set to "foo", and someField would be set to the value that was previously in field4.

Then I tried:

insert overwrite table ddb_table select field1, field2, field3, "foo" as someField, field4 FROM ddb_table where someField = "";

This one worked for me. For some reason moving the field that I want to change from the end of the list of fields to somewhere in the middle of the list of fields seemed to make it work.