如何在SQL查詢中添加一列，結果

Question

我有一個SQL statment這樣的選擇：

SELECT a.link_id, a.Speed_Limit_1, a.Speed_Limit_2, a.speed_limit_source, g.autos, g.trucks, g.motorcycles, 'vehicleType' as vehicleType 

FROM g, f, d, a 

WHERE f.access_id = g.access_id 
AND d.condition_id = f.condition_id 
AND g.access_id = a.access_id 

結果：

link_id ......汽車......卡車...摩托車......... vehicleTypes

---

1 .......... | .......ÿ.... | .. ..Y ...... | .....ň................. | .............？

2 .......... | ....... Y .... | .... Y ...... | ..... Y ... .............. | .............？

3 .......... | ....... Y .... | .... Y ...... | ..... N ... .............. | .............？

4 .......... | ....... Y .... | .... N ...... | ..... Y ... .............. | .............？

我會加列「vehicleTypes這裏面列應該是：

0，如果汽車，卡車和摩托車被允許（例如，行2）

1，如果只是汽車被允許

2如果只有卡車被允許

3如果只有摩托車被允許

我怎樣才能做到這一點？

Answer 1

這應該這樣做。 我添加了一個ELSE -1來表示它不符合任何條件。

SELECT 
    a.link_id, 
    a.Speed_Limit_1, 
    a.Speed_Limit_2, 
    a.speed_limit_source, 
    g.autos, g.trucks, 
    g.motorcycles, 

    CASE 
     WHEN g.autos = 'Y' AND g.trucks = 'Y' AND g.motorcycles = 'Y' THEN 0 
     WHEN g.autos = 'Y' AND g.trucks = 'N' AND g.motorcycles = 'N' THEN 1 
     WHEN g.autos = 'N' AND g.trucks = 'Y' AND g.motorcycles = 'N' THEN 2 
     WHEN g.autos = 'N' AND g.trucks = 'N' AND g.motorcycles = 'Y' THEN 3 
     ELSE -1 
    END as vehicleTypes 

FROM g, f, d, a 

WHERE f.access_id = g.access_id 
AND d.condition_id = f.condition_id 
AND g.access_id = a.access_id 

Answer 2

你應該使用Oracle的CASE WHEN塊

例如： https://www.techonthenet.com/oracle/functions/case.php