LeetCode（数据库）- 找到遗失的ID

-- 解决方案(1)
WITH t1 as (
    SELECT 1 as a
    UNION ALL SELECT 2
    UNION ALL SELECT 3
    UNION ALL SELECT 4
    UNION ALL SELECT 5
    UNION ALL SELECT 6
    UNION ALL SELECT 7
    UNION ALL SELECT 8
    UNION ALL SELECT 9
),
t2 as (
    SELECT 0 as b
    UNION ALL SELECT 1
    UNION ALL SELECT 2
    UNION ALL SELECT 3
    UNION ALL SELECT 4
    UNION ALL SELECT 5
    UNION ALL SELECT 6
    UNION ALL SELECT 7
    UNION ALL SELECT 8
    UNION ALL SELECT 9
),
t3 as (
    SELECT 10*a + 1*b as NUMBERS FROM t1, t2
    UNION ALL SELECT 100
    UNION ALL SELECT a FROM t1
)
SELECT NUMBERS AS 'ids' FROM t3
WHERE NUMBERS < (SELECT MAX(customer_id) FROM Customers)
AND NUMBERS NOT IN (SELECT customer_id FROM Customers)
ORDER BY NUMBERS ASC
-- 解决方案(2)
WITH RECURSIVE t AS (SELECT 1 num 
UNION ALL
SELECT num + 1 FROM t WHERE num < 100)
SELECT num ids
FROM t
WHERE num NOT IN (SELECT customer_id FROM Customers) AND num < (SELECT customer_id FROM Customers ORDER BY customer_id DESC LIMIT 1)