解决：ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list等问题

问题描述：

不同数据库中报错信息略有差别；

MySQL中报错：

Expression #1 of ORDER BY clause is not in SELECT list, references column 'public.student.id' which is not in SELECT list; this is incompatible with DISTINCT

PostgreSQL报错：

ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list

错误原因：

当使用distinct函数时排序字段没有出现在select后面；

举例：

表数据：

错误示例：

//可以看到排序字段是id，但是id没有出现在select distinct后面，所以会报错
select distinct name,age,class from student where name = '张三' order by id;

正确示例：

将排序字段id也添加到select distinct后面输出就好了

select distinct id, name,age,class from student where name = '张三' order by id;

示例结果：