Show unique first names from the patients table which only occurs once in the list.

To answer your question, I'm assuming you're using SQL. Here's a step-by-step guide on how to get unique first names from the patients table which only occur once in the list:

1. First, you need to count the number of occurrences of each first name in the patients table. You can do this using the GROUP BY clause in SQL. Here's an example:

SELECT first_name, COUNT(*) 
FROM patients 
GROUP BY first_name;

This will give you a list of first names and the number of times each one appears in the table.

2. Next, you want to filter this list to only include first names that appear once. You can do this using the HAVING clause in SQL, which allows you to filter on aggregate functions (like COUNT). Here's how you can do it:

SELECT first_name, COUNT(*) 
FROM patients 
GROUP BY first_name
HAVING COUNT(*) = 1;

This will give you a list of unique first names that only appear once in the patients table.