mybatis中判断某个字段是否为null或空

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本文介绍在MyBatis中如何实现IFNULL等条件判断功能，通过CASE...WHEN...THEN...ELSE...END语句替代IFNULL函数进行空值检查及长度判断。

MySql 里的IFNULL、NULLIF和ISNULL用法

mybatis不能使用IFNULL这些函数，可以用case . . . when . . . then . . . else . . . end代替

select id,is_topic_on as topicOn,topic_name as topicName,topic_recommend as topicRecommend,topic_introduction as topicIntroduction,topic_group as topicGroup,
        CASE WHEN (topic_user is null || (LENGTH(trim(topic_user))=0))THEN 0 ELSE 1 END as topicUser,CASE WHEN ((topic_community is null) or (LENGTH(trim(topic_community))=0)) THEN 0 ELSE 1 END as topicCommunity
        from tbl_community_topic where id=#{id}