Question

我想进行更新，只更新受影响的值，但我的更新查询有联接，因此where exists无法正常工作。

update semester_workload tA
set tA.account = (SELECT DISTINCT (t2.WORKING - t2.WORKLOAD) FROM SEMESTER_WORKLOAD t1
        join SEMESTER_WORKLOAD t2 on t1.ID_LECTURER = t2.ID_LECTURER
        WHERE t2.ACADEMIC_SEMESTER = 'WS10' AND tA.ID_SW = t2.ID_SW);
where exists (SELECT 1 FROM SEMESTER_WORKLOAD t1        
        join SEMESTER_WORKLOAD t2 on t1.ID_LECTURER = t2.ID_LECTURER
        WHERE t2.ACADEMIC_SEMESTER = 'WS10' AND tA.ID_SW = t2.ID_SW);

此代码无法正常工作，因为它显然无法在join子句后识别where exists。

Answer 1

只是一个简单的语法错误。在window.open子句之前有一个多余的半冒号：

where exists

Answer 2

你有一个＆＃34 ;;＆＃34;过量。请注意，您不需要连接同一个表三次，您可以这样做：

UPDATE SEMESTER_WORKLOAD t1
set t1.account = 
(
   SELECT t2.WORKING - t2.WORKLOAD FROM SEMESTER_WORKLOAD t2
   WHERE 
   (t1.ID_LECTURER, t1.ID_SW, 'WS10')=(t2.ID_LECTURER, t2.ID_SW, t2.ACADEMIC_SEMESTER) 
   FETCH FIRST ROWS ONLY
)
where exists 
(
   SELECT * FROM SEMESTER_WORKLOAD t2
   WHERE 
   (t1.ID_LECTURER, t1.ID_SW, 'WS10')=(t2.ID_LECTURER, t2.ID_SW, t2.ACADEMIC_SEMESTER) 
)

如何使用join在db2中更新

2 个答案: