Question

我想加入两个表格，并显示年份（日期），总数和车辆类型。如果year和vehicle_type相同则应合并其总数。这是我的疑问。

select extract(year from ra.roadAccident_date) as 'Year', 
       c.casualties_death + c.casualties_serious + c.casualties_minor as 'Total',
       ra.vehicle_type as 'Types of Vehicle'
from casualties c
join roadAccidents ra
on (c.accident_id = ra.accident_id)

我的结果是

Year  Total Types of Vehicle
2014    6   taxi
2014    9   lorry
2014    3   bus
2014    16  bus
2015    7   taxi
2015    5   lorry
2015    7   lorry
2016    2   bus
2016    5   lorry
2016    9   bus

对于2014年，我希望将车型总线合并为一行，总共19行。我尝试了多种group by方法，但找不到我想要的方法。

Answer 1

我不明白为什么一个简单的GROUP BY不起作用：

SELECT
    EXTRACT(YEAR FROM ra.roadAccident_date) AS 'Year',
    SUM(c.casualties_death + c.casualties_serious + c.casualties_minor) AS 'Total',
    ra.vehicle_type AS 'Types of Vehicle'
FROM casualties c
INNER JOIN roadAccidents ra
    USING accident_id
GROUP BY ra.vehicle_type, YEAR(ra.roadAccident_date)

Answer 2

将整个事物（作为子查询）用分组外部包裹，如

Select yr,vtype, sum(total) as tot from 
(
select extract(year from ra.roadAccident_date) as yr, 
   c.casualties_death +c.casualties_serious+c.casualties_minor as total
   ra.vehicle_type as vtype
from casualties c
join roadAccidents ra on (c.accident_id = ra.accident_id)
) stats group by yr, vtype

如果其他2列相同，则MySql连接表并添加列

2 个答案: