SQL将一个表的多条记录合并成另一表的多列

Question

I am working in SQL and have a destination table:

Event ID (key) |   Road    |     total count  |     motorcycles   |    cars    |   trucks   |   bus

And I have a record like table:

[Event ID    |    mode of transport      |       count
1           |      bus                  |          3
1           |      cars                 |         20
1           |      trucks               |          2 
1           |      motorcycles          |          5
2           |      bus                  |          1
2           |      cars                 |          12 
2           |      motorcycles          |          1][1]

(combination of Event ID and mode of transport combination is unique)

How do I combine the data from the second table into the first easily as result:

Event ID (key) |   Road    |     total count    |     motorcycles   |    cars    |   trucks   |   bus
1              |     ...   |      ...           |        5          |     20     |    2       |    3
2              |     ...   |      ...           |        1          |     12     |            |    1  

I am looking for a way that can incorporate the record data from the second table in one SQL structure / statement. Thank you!

Answer 1

You can use conditional aggregation:

select eventid, road,
       sum(count) as total_count,
       sum(case when mode = 'motorcycles' then count end) as cnt_motorcycles,
       sum(case when mode = 'car' then count end) as cnt_car,
       sum(case when mode = 'bus' then count end) as cnt_bus,
       sum(case when mode = 'truck' then count end) as cnt_truck
from t
group by eventid, road;