mysql 中int为null值 进行的比较

起始sql

select * from t_rabbit where sex = 0 and status = 0 and breed_count <= 3 AND is_grow = 1 
AND father_id <> 4

查询结果

null是查不出的
判断式中，不论 null =0 仍是null <> 0 ，结果都是false。
因此改为这样比较好

最终sql：

select * from t_rabbit where sex = 0 and status = 0 and breed_count <= 3 AND is_grow = 1 
AND ( father_id <> 4 or father_id is null )