数据库捞取不相等数据情况

select * from a 
    left join b on a.id =b.id 
    where a.name != b.name;

以上sql，粗看没啥毛病，实际分析数据，你会发现b.name或者a.name字段如果为空值，你讲捞取不出来。

修改如下：

select * from a 
    left join b on a.id =b.id 
    where 1=1
       or ( a.name != b.name and a.name is not null and b.name is not null)
       or (a.name is not null and b.name is null)
       or (b.name is not null and a.name is null);

生产中，遇见这种业务需要特殊优化，执行效率实在是差，本身就符合索引。