join for records that are atleast present in another table once code example
Example: join to find results not in another table
SELECT t1.name
FROM table1 t1
LEFT JOIN table2 t2 ON t2.name = t1.name
WHERE t2.name IS NULL
SELECT t1.name
FROM table1 t1
LEFT JOIN table2 t2 ON t2.name = t1.name
WHERE t2.name IS NULL