Question

我有sql查询，其中我正在传递学生ID＆＃39; IN＆＃39;条款。如果没有与给定id匹配的记录，则不返回任何内容。即使没有匹配的记录，我希望查询返回虚假或不存在的内容

//伪查询（为了简洁起见，我限制查询一个表，实际查询涉及其他表。）

Select student_id from STUDENTS  WHERE s.student_id in (?,?,?);

Answer 1

申请OR is null

Select s.student_id 
from STUDENTS   s
WHERE s.student_id in (?,?,?)
  or s.student_id is null;

如果加入，请使用左连接：

select s.student_id
from students s
left join othertable o
  on o.something = s.something
WHERE s.student_id in (?,?,?)
  or s.student_id is null;

如果学生在右边：

select s.student_id
from othertable o
left join students s
  on o.something = s.something
  and s.student_id in (?,?,?) -- we put this into the join clause so we don't need the "or is null"
;

Answer 2

IF EXISTs(Select student_id from STUDENTS  WHERE s.student_id in (?,?,?))
  BEGIN 
    Select student_id from STUDENTS  WHERE s.student_id in (?,?,?)
 END
  ELSE 
    select 0

SQL：即使没有匹配也返回一些值

2 个答案: