custom column in query editor

Hi,  I hope someone can help me on this.  I have screenshot below of my sample data.

1) How can I do in Query Editor to convert "0" to 1 in column B?  Because I tried adding Conditional column but other decimals like 0.000011 are being converted to 1 too?  I only wanted exactly 0 to be converted to 1

2) I have added Custom column in Query Editor because I want per row to divide A and B but I'm getting infinity if there's 0.  I would just like the result to be null or convert B column with exactly 0 to 1 so it will not result to infinity.  I tried "try .... otherwise" in custom column but it did not work.