我應該使用哪個SQL子句？

Question

我有這樣一個表中火鳥：

+-----------+----+------+ 
|vehiclename|oil |volume| 
+-----------+----+------+ 
|v1   |oil1|12 | 
+-----------+----+------+ 
|v2   |oil2|26 | 
+-----------+----+------+ 
|v3   |oil1|45 | 
+-----------+----+------+ 
|v1   |oil2|78 | 
+-----------+----+------+ 
|v2   |oil3|95 | 
+-----------+----+------+ 

，我想作爲

+-----------+----+----+----+ 
|vehiclename|oil1|oil2|oil3| 
+-----------+----+----+----+ 
|v1   |12 |78 |0 | 
+-----------+----+----+----+ 
|v2   |0 |26 |95 | 
+-----------+----+----+----+ 
|v3   |45 |0 |0 | 
+-----------+----+----+----+ 

我已經嘗試使用該表存在的情況下聲明，但沒有結果子句。 任何想法？

Answer 1

select vehiclename, 
     sum(case when oil = 'oil1' then volume end) as oil_1, 
     sum(case when oil = 'oil2' then volume end) as oil_2, 
     sum(case when oil = 'oil3' then volume end) as oil_3 
from the_table 
group by vehiclename 
order by vehiclename; 

如果添加新油種，你需要添加一個CASE語句可以在oil欄中顯示的每個值。

如果您需要自動執行此操作，則需要使用動態SQL，其中您首先檢索oil列的不同值，然後按照上述解決方案中的模式創建SQL語句。然後運行該動態SQL語句。

Answer 2

SELECT vehiclename, 
sum(CASE WHEN oil = 'oil1' THEN volume END) AS oil1, 
sum(CASE WHEN oil = 'oil2' THEN volume END) AS oil2, 
sum(CASE WHEN oil = 'oil3' THEN volume END) AS oil3 
FROM test 
GROUP BY vehiclename; 

SQL Fiddle [MySQL version]