Access Value between ranges
Try something along the lines of:

UPDATE Table2 
INNER JOIN Table1 ON Table2.[My Values] &gt;= Table1.Start AND Table2.[My Values] &lt; Table1.End
SET Table2.Bucket = Table1.Bucket;


Essentially, we get the value from Table1 by comparing the My Values field in Table2 to see if it is between Table1.Start and Table1.End

This will update the entire Table2 in a single statement, and shows the power of set-based approaches to data vs what is referred to as "row by agonizing row" or RBAR.  See https://www.simple-talk.com/sql/t-sql-programming/rbar--row-by-agonizing-row/ for a great explanation of that.