How show mysql query without NULL?

Question

How show mysql query without NULL?

I want to show my query where "LAG(title) OVER(PARTITION BY emp_no)" IS NOT NULL, I need only titles.emp_no = "LAG(title) OVER(PARTITION BY emp_no)"

My query:

SELECT titles.emp_no, LAG(title) OVER(PARTITION BY emp_no)
FROM titles;

Output:

Answer 1

Subquery your current query and filter based on the lag value:

WITH cte AS (
    SELECT emp_no, LAG(title) OVER (PARTITION BY emp_no ORDER BY <col>) lag_title
    FROM titles
)

SELECT emp_no, lag_title
FROM cte
WHERE lag_title IS NOT NULL;

Notice that I added an ORDER BY clause to LAG, without which is does not make much sense.