mysql查询的唯一结果

我希望父项在此查询中是唯一的：

select 
  *, 
  (select state_name 
   from tbl_states 
   where state_id = tbl_cities.parent_id) as parent 
from 
  tbl_cities 
ORDER BY 
  parent

我尝试使用：

select 
  *, 
  DISTINCT (select state_name 
            from tbl_states 
            where state_id = tbl_cities.parent_id) as parent 
from 
  tbl_cities 
ORDER BY 
  parent

---

但是它给出了一个错误。

术语顺序不正确。你想要

select DISTINCT * ...

---

在语法上，您应该将DISTINCT放在子选择中：

select * , 
 (select DISTINCT state_name 
  from tbl_states 
  where state_id = tbl_cities.parent_id) as parent 
from tbl_cities ORDER BY parent

我不明白为什么会有多个状态，它们真的是重复的同一个状态吗？ 如果存在不同的状态，那么您就有不同的问题。在这种情况下，就语法而言，以下操作将起作用：

select * , 
 (select MAX(state_name) 
  from tbl_states 
  where state_id = tbl_cities.parent_id) as parent 
from tbl_cities ORDER BY parent

---

但是语义可能不符合您的要求。

像这样重新编写，并获得符合ANSI标准的额外好处

select 
  c.*, parent.state_name
from 
  tbl_cities c
  left join (
    select 
      state_id, state_name 
    from 
      tbl_states 
    group by 
      state_id, state_name
  ) as parent 
  on parent.state_id = c.parent_id
order by 
  parent.state_name;

---

抛出了什么错误？1064-您的SQL语法有错误；检查与您的MySQL服务器版本对应的手册，以获得正确的语法，以便在第1行中使用“DISTINCT select state_name from tbl_states，其中state_id=tbl_cities.parent_i”附近的“DISTINCT select state_name from tbl_states，其中state_id=tbl_cities