我有一个包含三列（lending_id int, installment_n serial int, status text）的表格，我想知道如何为每个lending_id检索WAITING_PAYMENT (status)的最大差距。
对于以下示例：
lending_id | installment_n | status
71737 1 PAID
71737 2 PAID
71737 3 PAID
71737 4 PAID
71737 5 PAID
71737 6 WAITING_PAYMENT
71737 7 WAITING_PAYMENT
71737 8 WAITING_PAYMENT
71737 9 WAITING_PAYMENT
71737 10 WAITING_PAYMENT
71737 11 WAITING_PAYMENT
71737 12 WAITING_PAYMENT
71737 13 WAITING_PAYMENT
71737 14 WAITING_PAYMENT
71737 15 WAITING_PAYMENT
71737 16 WAITING_PAYMENT
71737 17 WAITING_PAYMENT
71737 18 WAITING_PAYMENT
71737 19 WAITING_PAYMENT
71737 20 WAITING_PAYMENT
71737 21 WAITING_PAYMENT
354226 1 PAID
354226 2 PAID
354226 3 WAITING_PAYMENT
354226 4 WAITING_PAYMENT
354226 5 WAITING_PAYMENT
354226 6 WAITING_PAYMENT
354226 7 PAID
354226 8 WAITING_PAYMENT
354226 9 WAITING_PAYMENT
354226 10 WAITING_PAYMENT
354226 11 WAITING_PAYMENT
354226 12 WAITING_PAYMENT
354226 13 WAITING_PAYMENT
354226 14 WAITING_PAYMENT
354226 15 WAITING_PAYMENT
我想知道如何检索：
lending_id | count
71737 | 16
354226 | 8
自71737起，它将从第6至21（16）期考虑 对于354226，8和15（8）之间的差距。
答案 0 :(得分：2)
您可以使用相关子查询和一些其他逻辑：
select lending_id, max(cnt)
from (select lending_id, t.next_in, count(*) as cnt
from (select t.*,
(select min(t2.installment_n)
from t t2
where t2.lending_id = t.lending_id and t2.installment_n > t.installment_n and
t2.status <> 'WAITING_PAYMENT'
) as next_in
from t
where t.status = 'WAITING_PAYMENT'
) t
group by lending_id, t.next_in
) lt
group by lending_id;
这是如何工作的？最里面的子查询得到的下一个分期编号不是WAITING_PAYMENT - 或NULL，如果没有。这标识了所有顺序WAITING_PAYMENT记录组。
中间子查询计算每个组中的数字。外部查询占用最大值。
答案 1 :(得分：1)
下面的SQL应该可以做到这一点，并且易于阅读和理解时尚：
select t1.lending_id, max(t1.installment_n) - min(t1.installment_n) as count
from table t1
where t1.status = 'WAITING_PAYMENT'
and t1.installment_n >
(SELECT max(t2.installment_n) FROM table t2 where t2.lending_id = t1.lending_id and t2.status = 'PAID')
group by lending_id;
如有任何进一步的澄清，请不要犹豫，问我。
泰德。
答案 2 :(得分：1)
这是一种基于模仿row_number()的方法，该方法适用于不支持窗口函数的MySQL版本（计划将窗口函数包含在MySQL v8.x中）。
这种方法的结果将揭示关于最长序列的更多事实而不仅仅是计数。有关详细信息，请参阅下面的结果。
MySQL 5.6架构设置：
CREATE TABLE Table1
(`lending_id` int, `installment_n` int, `status` varchar(15))
;
INSERT INTO Table1
(`lending_id`, `installment_n`, `status`)
VALUES
(71737, 1, 'PAID'),
(71737, 2, 'PAID'),
(71737, 3, 'PAID'),
(71737, 4, 'PAID'),
(71737, 5, 'PAID'),
(71737, 6, 'WAITING_PAYMENT'),
(71737, 7, 'WAITING_PAYMENT'),
(71737, 8, 'WAITING_PAYMENT'),
(71737, 9, 'WAITING_PAYMENT'),
(71737, 10, 'WAITING_PAYMENT'),
(71737, 11, 'WAITING_PAYMENT'),
(71737, 12, 'WAITING_PAYMENT'),
(71737, 13, 'WAITING_PAYMENT'),
(71737, 14, 'WAITING_PAYMENT'),
(71737, 15, 'WAITING_PAYMENT'),
(71737, 16, 'WAITING_PAYMENT'),
(71737, 17, 'WAITING_PAYMENT'),
(71737, 18, 'WAITING_PAYMENT'),
(71737, 19, 'WAITING_PAYMENT'),
(71737, 20, 'WAITING_PAYMENT'),
(71737, 21, 'WAITING_PAYMENT'),
(354226, 1, 'PAID'),
(354226, 2, 'PAID'),
(354226, 3, 'WAITING_PAYMENT'),
(354226, 4, 'WAITING_PAYMENT'),
(354226, 5, 'WAITING_PAYMENT'),
(354226, 6, 'WAITING_PAYMENT'),
(354226, 7, 'PAID'),
(354226, 8, 'WAITING_PAYMENT'),
(354226, 9, 'WAITING_PAYMENT'),
(354226, 10, 'WAITING_PAYMENT'),
(354226, 11, 'WAITING_PAYMENT'),
(354226, 12, 'WAITING_PAYMENT'),
(354226, 13, 'WAITING_PAYMENT'),
(354226, 14, 'WAITING_PAYMENT'),
(354226, 15, 'WAITING_PAYMENT')
;
查询1 ：
select lending_id, status, start_at_inst, end_at_inst, inst_count
from (
select IF(@prev_value=lending_id, @rn:=@rn+1 , @rn:=1) AS rn
, lending_id, status, start_at_inst, end_at_inst, inst_count
, @prev_value := lending_id z
from (
select lending_id
, status
, grpby
, min(installment_n) start_at_inst
, max(installment_n) end_at_inst
, (max(installment_n) + 1) - min(installment_n) inst_count
from (
select
IF(@prev_value=concat_ws(',',lending_id,status), @rn:=@rn+1 , @rn:=1) AS rn
, t.*
, installment_n - @rn grpby
, @prev_value := concat_ws(',',lending_id,status) z
from Table1 t
cross join (
select @rn := 0 , @prev_value := ''
) vars
order by lending_id, status,installment_n ASC
) d1
group by lending_id, status, grpby
) d2
cross join (
select @rn := 0 , @prev_value := ''
) vars
order by lending_id, inst_count DESC
) d3
where rn = 1
<强> Results ：
| lending_id | status | start_at_inst | end_at_inst | inst_count |
|------------|-----------------|---------------|-------------|------------|
| 354226 | WAITING_PAYMENT | 8 | 15 | 8 |
| 71737 | WAITING_PAYMENT | 6 | 21 | 16 |
虽然在V8.x的MySQL处于生产版本之前你不能使用row_number（）;但是对于db已经支持它的用户，以及可用的MySQL用户，使用row_number（）的方法与使用row_number（）相同，我认为它比@variable方法更有效。
select
lending_id, status, start_at_inst, end_at_inst, inst_count
from (
select
lending_id
, status
, grpby
, min(installment_n) start_at_inst
, max(installment_n) end_at_inst
, (max(installment_n) + 1) - min(installment_n) inst_count
, row_number() over(partition by lending_id order by (max(installment_n) + 1) - min(installment_n) DESC) rn
from (
select
t.*
, installment_n - row_number() over(partition by lending_id, status order by installment_n) grpby
from Table1 t
) d1
group by
lending_id, status, grpby
) d2
where rn = 1
;
<强>结果：
lending_id | status | start_at_inst | end_at_inst | inst_count
---------: | :-------------- | ------------: | ----------: | ---------:
71737 | WAITING_PAYMENT | 6 | 21 | 16
354226 | WAITING_PAYMENT | 8 | 15 | 8
dbfiddle（mariadb_10.2）here