If cell in Col A is blank substitute with cell in Col B

I’m attempting to combine two columns from another sheet into one through the QUERY function. My plan is to make it so if a cell in Col A is empty then a cell in Col B will be substituted.

However, due to my inexperience, I am unable to create the right formula. If anyone can help, it will be much appreciated…

Here is a diagram:


I know about IF(ISBLANK(Sheet1!A1), Sheet1!$B1, Sheet1!$A1) but I’m looking for an alternative method that does not require me to have to copy and paste this formula in Sheet 2 for every row.