题解 | SQLW6 统计所有课程参加培训人次

WITH t1 AS (
    SELECT length(course) AS len
    FROM cultivate_tb
    WHERE course IS NOT NULL
),
t2 AS (
    SELECT
        CASE WHEN len = 7 THEN 1
            WHEN len = 15 THEN 2
            WHEN len = 23 THEN 3
        END AS num
    FROM t1
)SELECT SUM(num) AS staff_nums FROM t2;

# 这道题的关键在于提前知道课程类别和数量，因此投机取巧用长度进行判断数量！