MySQL运行total仅使用硬编码整数

我有下面的SQL，它不能像我想象的那样工作

SET @runtot:=0;
select 
q1.week,
(@runtot := @runtot + cast(q1.flying_hours as SIGNED)) as flying_hours,
q1.flying_hours as weekly_hours
from
(
select 
date_format(d.date,"%x%v") as week,
cast(ceil(sum(fh.engine_minutes)/60) as SIGNED) as flying_hours
from dates d 
left join flyinghours fh on date_format(fh.flight_start, "%x%v") = date_format(d.date,"%x%v")
where d.`date` >= "2019-01-01"
and d.date <= date_add(now(), interval 1 month)
group by date_format(d.date,"%x%v")
) q1
limit 20

然而，我将飞行小时数替换为子查询中的硬编码整数

SET @runtot:=0;
select 
q1.week,
(@runtot := @runtot + cast(q1.flying_hours as SIGNED)) as flying_hours,
q1.flying_hours as weekly_hours
from
(
select 
date_format(d.date,"%x%v") as week,
5 as flying_hours
from dates d 
left join flyinghours fh on date_format(fh.flight_start, "%x%v") = date_format(d.date,"%x%v")
where d.`date` >= "2019-01-01"
and d.date <= date_add(now(), interval 1 month)
group by date_format(d.date,"%x%v")
) q1
limit 20

---

问题在于某些值为空。当我使用ifnull（）替换为零时，一切都正常

SET @runtot:=0;
select 
q1.week,
@runtot := @runtot + ifnull(q1.flying_hours,0) as flying_hours,
q1.flying_hours as weekly_hours
from
(
select 
date_format(d.date,"%x%v") as week,
cast(ceil(sum(fh.engine_minutes)/60) as SIGNED) as flying_hours
from dates d 
left join flyinghours fh on date_format(fh.flight_start, "%x%v") = date_format(d.date,"%x%v")
where d.`date` >= "2019-01-01"
and d.date <= date_add(now(), interval 1 month)
group by date_format(d.date,"%x%v")
) q1
limit 20

---

替代解决方案：升级到感谢您的建议，但目前我希望/需要保持与5.x的兼容性，但没有理由不让它正常工作。

"week"  "flying_hours"  "weekly_hours"
"201901"    "5" "5"
"201902"    "10"    "5"
"201903"    "15"    "5"
"201904"    "20"    "5"
"201905"    "25"    "5"
"201906"    "30"    "5"
"201907"    "35"    "5"
"201908"    "40"    "5"
"201909"    "45"    "5"
"201910"    "50"    "5"
"201911"    "55"    "5"
"201912"    "60"    "5"
"201913"    "65"    "5"
"201914"    "70"    "5"
"201915"    "75"    "5"
"201916"    "80"    "5"
"201917"    "85"    "5"
"201918"    "90"    "5"
"201919"    "95"    "5"
"201920"    "100"   "5"

SET @runtot:=0;
select 
q1.week,
@runtot := @runtot + ifnull(q1.flying_hours,0) as flying_hours,
q1.flying_hours as weekly_hours
from
(
select 
date_format(d.date,"%x%v") as week,
cast(ceil(sum(fh.engine_minutes)/60) as SIGNED) as flying_hours
from dates d 
left join flyinghours fh on date_format(fh.flight_start, "%x%v") = date_format(d.date,"%x%v")
where d.`date` >= "2019-01-01"
and d.date <= date_add(now(), interval 1 month)
group by date_format(d.date,"%x%v")
) q1
limit 20

"week"  "flying_hours"  "weekly_hours"
"201901"    "0" \N
"201902"    "0" \N
"201903"    "0" \N
"201904"    "0" \N
"201905"    "20"    "20"
"201906"    "29"    "9"
"201907"    "29"    \N
"201908"    "29"    \N
"201909"    "29"    \N
"201910"    "29"    \N
"201911"    "29"    \N
"201912"    "29"    \N
"201913"    "29"    \N
"201914"    "29"    \N
"201915"    "29"    \N
"201916"    "29"    \N
"201917"    "36"    "7"
"201918"    "75"    "39"
"201919"    "168"   "93"
"201920"    "177"   "9"