SQL在CASE语句为真时返回另一个表的值

我想编写一个SQL语句，该语句基于具有三种可能结果的CASE语句返回一个值。SQL在CASE语句为真时返回另一个表的值

1）如果该列值与“C0”则返回两列的级联在表

2）如果该列与“L0”开始开始再取在另一列（_PARENT_PROJECT_NUMBER的值）在那一行，看看这个值是否在另一个表中。如果不是，则返回值_PARENT_PROJECT_NUMBER。

3）如果_PARENT_PROJECT_NUMBER确实驻留在另一个表中，则返回另一个表“Rollup_Project_Mapping”中列“Rollup_Project”中的值。

我写下面的语句工作正常，除了第12行，"Rollup_Project_Mapping"."Rollup_Project"我希望它返回其他表的值，如果_PARENT_PROJECT_NUMBER在另一个表中找到。这里是错误信息：

ERROR: syntax error at or near "FROM" 
LINE 12:  FROM "Rollup_Project_Mapping"."Rollup_Project"

有没有人知道我可以如何返回CASE陈述的这一部分是真的时在另一个表中的值？

SELECT 
CASE 
    WHEN LEFT("_PROJECT_NUMBER",2)='C0' THEN 
    '('||"_PROJECT_NUMBER"||') '||"_PROJECT_DESCRIPTION" 
    WHEN LEFT("_PROJECT_NUMBER",2)='L0' THEN 
    CASE 
     WHEN (SELECT "Rollup_Project" FROM "Project_Rollup_Mapping" WHERE "PA_ACCOUNTED_TEST"."_PARENT_PROJECT_NUMBER" = "Project_Rollup_Mapping"."Project") IS NOT NULL THEN 
     "Rollup_Project_Mapping"."Rollup_Project" 
    ELSE "_PARENT_PROJECT_NUMBER" 
    END 
END AS Rollup_Project2 
FROM "PA_ACCOUNTED_TEST";

来源

2016-03-20 christopheralan88

只需使用一组WHEN/THEN报表和EXISTS：

SELECT (CASE WHEN LEFT("_PROJECT_NUMBER",2) = 'C0' 
      THEN '('||"_PROJECT_NUMBER"||') '||"_PROJECT_DESCRIPTION" 
      WHEN LEFT("_PROJECT_NUMBER",2) = 'L0' AND 
        EXISTS (SELECT "Rollup_Project" FROM "Project_Rollup_Mapping" WHERE "PA_ACCOUNTED_TEST"."_PARENT_PROJECT_NUMBER" = "Project_Rollup_Mapping"."Project") 
        THEN (SELECT "Rollup_Project" FROM "Project_Rollup_Mapping" WHERE "PA_ACCOUNTED_TEST"."_PARENT_PROJECT_NUMBER" = "Project_Rollup_Mapping"."Project") 
      ELSE "_PARENT_PROJECT_NUMBER" 
     END) AS Rollup_Project2 
FROM "PA_ACCOUNTED_TEST";

来源

2016-03-20 02:52:28

谢谢！完美工作！ – christopheralan88

我适应原来的SQL语句基于@Gordon Linoff答案的情况下，任何人合作想让它作为另一种选择：

SELECT 
CASE 
    WHEN LEFT("_PROJECT_NUMBER",2)='C0' THEN 
    '('||"_PROJECT_NUMBER"||') '||"_PROJECT_DESCRIPTION" 
    WHEN LEFT("_PROJECT_NUMBER",2)='L0' AND (SELECT "Rollup_Project" FROM "Project_Rollup_Mapping" WHERE "PA_ACCOUNTED_TEST"."_PARENT_PROJECT_NUMBER" = "Project_Rollup_Mapping"."Project") IS NOT NULL THEN 
    (SELECT "Rollup_Project" FROM "Project_Rollup_Mapping" WHERE "PA_ACCOUNTED_TEST"."_PARENT_PROJECT_NUMBER" = "Project_Rollup_Mapping"."Project") 
    ELSE "_PARENT_PROJECT_NUMBER" 
END AS Rollup_Project2 
FROM "PA_ACCOUNTED_TEST";

来源

2016-03-21 00:41:57 christopheralan88

SQL在CASE语句为真时返回另一个表的值

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