您只能使用一组WHEN
/THEN
语句和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";