相关疑难解决方法(0)

我做了一个外连接并在informix数据库中成功执行但我在我的代码中得到以下异常:

DataTable dt = TeachingLoadDAL.GetCoursesWithEvalState(i, bat);

无法启用约束.一行或多行包含违反非null,唯一或外键约束的值.

我知道这个问题,但我不知道如何解决它.

我在外连接上创建的第二个表包含一个复合主键,它在前一个外连接查询中为空.

编辑:

    SELECT UNIQUE a.crs_e,  a.crs_e  || '/ ' || a.crst crs_name, b.period,
           b.crscls, c.crsday, c.from_lect, c.to_lect,
           c.to_lect - c.from_lect + 1 Subtraction, c.lect_kind, e.eval, e.batch_no,
           e.crsnum, e.lect_code, e.prof_course
    FROM rlm1course a, rfc14crsgrp b, ckj1table c, mnltablelectev d,
         OUTER(cc1assiscrseval e)  
    WHERE a.crsnum = b.crsnum 
    AND b.crsnum = c.crsnum 
    AND b.crscls = c.crscls 
    AND b.batch_no = c.batch_no 
    AND c.serial_key = d.serial_key  
    AND c.crsnum = e.crsnum  
    AND c.batch_no = e.batch_no  
    AND d.lect_code= …