Question

搜索表格，看它是否包含X，如果它找不到X我需要它返回Y.这是我到目前为止所尝试的：

SELECT WHEN T1.X IS NULL THEN Y ELSE T1.X END AS XY 
FROM TABLE1 T1
LEFT JOIN TABLE2 T2 ON T1.X = T2.X
WHERE T1.X IN (A, B, C);

SELECT CASE WHEN T1.X IS NOT NULL THEN T1.X ELSE Y END AS XY
FROM TABLE1 T1
WHERE T1.X IN (A, B, C)
AND T1.X IN (
    SELECT T2.X
    FROM TABLE2 T2);

SELECT CASE WHEN EXISTS (SELECT X FROM TABLE1) THEN X ELSE Y END AS XY
FROM TABLE1 
WHERE X IN (A, B, C);

我返回0行，它找不到A，B或C，而不是Y.但如果它找到A，B或C，它会正确返回X.

Answer 1

简单UNION

SELECT X FROM TABLE1 WHERE X IN (A, B, C) 
UNION 
SELECT Y FROM SYSIBM.SYSDUMMY1 
WHERE NOT EXISTS (SELECT X FROM TABLE1 WHERE X IN (A, B, C))

Answer 2

我发现这可以与DB2一起使用：

SELECT A, B, 
Case C
WHEN 'Citron' THEN 'Lemon'
WHEN 'Charlie' THEN 'Name'
end as Choice, 
D
FROM TABLE with UR;

也可以使用DB2 Java驱动程序。

存在时的DB2案例

2 个答案: