Task: Text to Code
Input (English): Step 1: find the Invoice's CustomerId of Invoice table for which Total less than 20.
Step 2: find the LastName of Customer table whose Customer's CustomerId not one of the results of step 1
Output (English): SELECT T1.LastName FROM Customer AS T1 WHERE T1.CustomerId NOT IN ( SELECT T2.CustomerId FROM Invoice AS T2 WHERE T2.Total < 20 )