题解 | SQL241 删除emp_no重复的记录，只保留最小的id对应的记录。

WITH t1 AS (
    SELECT 
        *,
        DENSE_RANK() OVER(PARTITION BY emp_no ORDER BY id ASC) AS ranking
    FROM titles_test 
),
t2 AS(
    SELECT 
        id,
        emp_no,
        title,
        from_date,
        to_date
    FROM t1
    WHERE ranking = 1
)
DELETE FROM titles_test WHERE id NOT IN (SELECT id FROM t2);

# 这道题本意就是删除操作，因此可以使用delete命令！