SQL - 條件Where語句

Question

我有以下表和數據：

DECLARE @Temp TABLE (id int, city varchar(10), ref varchar(10)) 

INSERT INTO @Temp (id, city, ref) 
SELECT 1, 'London', 'GBP' UNION ALL 
SELECT 2, 'London', 'EUR' 

SELECT * 
FROM @Temp 
WHERE ((city = 'London' AND ref = 'GBP') OR (city = 'London' AND ref <> 'GBP')) 

這將返回：

1 London GBP 
2 London EUR 

我想要做的是檢查，其中城市= '倫敦' AND ref ='GBP'，如果沒有排位賽資格，那麼檢查一下這個城市是否是倫敦，ref是什麼，嘗試使用case但是沒有工作。

在這種情況下，我應該只得到行＃1。

感謝

Answer 1

select city, max(ref) 
from @Temp 
group by city 

或者

select city, ref 
from @Temp t1 
where t1.ref = 'GBP' 
    or not exists (select 1 from @Temp t2 
        where t2.city = t1.city 
        and t2.ref = 'GBP') 

Answer 2

剛剛回歸時，有沒有GPB行不包含GBP行，並使用NOT EXISTS：

SELECT * 
FROM @Temp 
WHERE (city = 'London' AND ref = 'GBP') OR (city = 'London' AND NOT EXISTS (SELECT * 
      FROM @Temp 
      WHERE city = 'London' AND ref = 'GBP')) 

• 見this fiddle

Answer 3

如果你正在處理一個記錄，那麼接下來應該工作：

SELECT TOP 1 * 
FROM @Temp 
WHERE city = 'London' 
ORDER BY CASE WHEN ref = 'GBP' THEN 0 ELSE 1 END 

Answer 4

SELECT * 
FROM @Temp 
WHERE city = 'London' AND ref = 'GBP' 
UNION 
SELECT * 
FROM @Temp 
WHERE NOT EXISTS (
    SELECT * 
    FROM @Temp 
    WHERE city = 'London' AND ref = 'GBP' 
) AND city = 'London' 

SELECTUNION後是有條件的地方。

Answer 5

您可以使用CASE WHEN：

SELECT * 
FROM @Temp 
WHERE 
    CASE 
    WHEN city = 'London' AND ref = 'GBP' THEN 1 
    WHEN city = 'London' AND ref <> 'GBP' AND NOT EXISTS(SELECT 1 FROM @Temp 
                 WHERE city = 'London' 
                 AND ref = 'GBP') THEN 1 
    ELSE 0 
END = 1 

LiveDemo

Answer 6

你可以NOT EXISTS類似嘗試：

SELECT * 
FROM @Temp 
WHERE ((city = 'London' AND ref = 'GBP') OR (city = 'London' AND ref <> 'GBP' 
     AND NOT EXISTS (SELECT * 
         FROM @Temp 
         WHERE city = 'London' AND ref = 'GBP'))) 

Answer 7

我認爲你可以處理的情況下訂購像這樣

SELECT TOP 1 * 
FROM @Temp t 
    CROSS APPLY -- The ordering logic write here 
    (
     SELECT 
      CASE 
       WHEN (city = 'London' AND ref = 'GBP') THEN 1 
       WHEN (city = 'London' AND ref <> 'GBP') THEN 2 
       -- Not match at all 
      END AS Value 
    ) orders 
WHERE orders.Value IS NOT NULL 
ORDER BY 
    CASE WHEN orders.Value IS NULL THEN 1 ELSE 0 END, 
    orders.Value