查询中未返回空值

Question

我有以下查询，我想排除“否”值。我想包括 N/A、Yes 和 null。 “No”、“Yes”、“N/A”和“null”是此列中的唯一值。当我运行查询时，它不会返回空值，但会返回“N/A”和“Yes”。

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select s.schoolid as "School Code", 
       sch.name as "School Name", 
       s.student_number as "Student Id", 
       s.lastfirst as "Name", 
       s.gender as "Gender", 
       s.grade_level as "Grade", 
       s.street as "Street", 
       s.city as "City", 
       s.state as "State", 
       s.zip as "Zip", 
       s.home_phone as "Home Phone" 
from u_students u 
  left join students s on u.studentsdcid = s.dcid
  left join schools sch on s.schoolid = sch.school_number
where s.grade_level in ('11','12')
  and s.enroll_status = '0'
  and U.Scs_Perm_Share_Military Not like 'No'
order by sch.name asc ;

Answer 1

如果 SELECT 语句除了测试其他值之外还测试空值，它必须包含一个 IS NULL 子句。同样正如其他人所说，您应该使用左连接条件而不是将过滤器放在 where 子句中：

select s.schoolid as "School Code", 
       sch.name as "School Name", 
       s.student_number as "Student Id", 
       s.lastfirst as "Name", 
       s.gender as "Gender", 
       s.grade_level as "Grade", 
       s.street as "Street", 
       s.city as "City", 
       s.state as "State", 
       s.zip as "Zip", 
       s.home_phone as "Home Phone" 
from u_students u 
  left join students s on u.studentsdcid = s.dcid
                      and s.grade_level in ('11','12')
                      and s.enroll_status = '0'
  left join schools sch on s.schoolid = sch.school_number
where (U.Scs_Perm_Share_Military IS NULL
       OR
       U.Scs_Perm_Share_Military <> 'No'
      )
order by sch.name asc ;