mysql 字段值为NULL仍然需要查出来

death114

　　QuestionAnswer表
　　Login表
　　
　　SELECT an.`answerId`,an.`loginId`,an.`ipAddress`,lg.viewName FROM `QuestionAnswer` as an,Login as lg where lg.loginId = an.loginId and `surveyId` = 14 
　　QuestionAnswer表中有loginId字段可能为NULL,这样关联查询为查不到.
　　解决方法1:
　　
　　SELECT DISTINCT an.`answerId`,an.`loginId`,an.`ipAddress`, CASE WHEN an.`loginId` IS NULL   THEN ' ' ELSE lg.viewName END AS viewName FROM  QuestionAnswer AS an,Login AS lg WHERE lg.loginId = an.loginId AND an.`surveyId` = 14 OR an.loginId IS NULL;




解决方法2:用union,稍候补上.