存在时的DB2案例

wvyml7n5 于 2022-11-07 发布在 DB2

关注(0)|答案(3)|浏览(155)

搜索一个表，看看它是否包含X，如果它没有找到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);

如果没有找到A、B或C，则返回0行，而不是Y。但如果找到了A、B或C，则确实正确地返回X。

db2

来源：https://stackoverflow.com/questions/41286721/db2-case-when-exists

3条答案

按热度按时间

6za6bjd01#

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))

赞(0）回复(0）举报 2022-11-07

7tofc5zh2#

我发现DB2可以使用以下代码：

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

也可以与DB2 java驱动程序一起使用。

赞(0）回复(0）举报 2022-11-07

bqjvbblv3#

这在DB2中用作记录存在性测试

SELECT
  CASE COUNT(*)
    WHEN 0 THEN 'FALSE'
    ELSE 'TRUE'
  END as IsRecordThere
FROM MYTABLE 
WHERE COL1 = 'whatever' AND COL2 = 'etc'

赞(0）回复(0）举报 2022-11-07

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存在时的DB2案例

3条答案

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