当CASE语句为true时，SQL返回另一个表的值

您只能使用一组

WHEN

THEN

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_Project2FROM "PA_ACCOUNTED_TEST";