Sql Check One List Against Another

I'd appreciate any pointers on how in SQL to check whether elements in one list also appear in another. List A = Live Customers in April List B = Live Customers in May How can I c

Solution 1:

Different ways to pull the results

SELECT customer
FROM ListA a 
WHERENOTEXISTS (SELECT1FROM ListB b WHERE a.customer=b.customer)

OR

SELECT a.customer
FROM ListA a 
  LEFTJOIN ListB b ON a.customer=b.customer
WHERE b.customer isnull

OR

SELECT customer
FROM ListA

exceptSELECT customer
FROM ListB

OR

SELECT customer
FROM ListA 
WHERE customer NOTIN (SELECT customer FROM ListB )

Solution 2:

Try the not in clause

example

select * 
from mytable 
where id notin (select id from table2)

this will return results that are not in another table. quick and simple