使用单个JOIN Select语句替换UNION的替代/替代

Question

我有一个名为posts的表格，我希望retrieve符合records中满足以下条件的所有select statement并返回single table -

select ID from posts where UserID= 23487 and postlevel <> 1
select ID from posts where ParentID in (select ID from posts where UserID= 23487 and postlevel <> 1)

现在，通过使用下面的UNION运算符，我可以返回一个表 -

select ID from posts where UserID= 23487 and postlevel <> 1
UNION 
select ID from posts where ParentID in (select ID from posts where UserID= 23487 and postlevel <> 1)

输出

在JOIN查询下方尝试但未获得预期结果并返回NULL -

select ID from posts cs
LEFT JOIN posts cs1 ON cs.ID = cs1.ID
where cs.UserID = 23487 and cs.PostLevel <>1 and cs.ParentID = cs1.ID

预期

我想使用JOIN或使用单个SELECT而不是UNION来获取记录，以获得所需的输出，如上所示。

Answer 1

您是否尝试在单个WHERE子句中将两个条件进行OR运算：

select ID
from posts
where
    (UserID = 23487 and postlevel <> 1) or
    (ParentID in (select ID from cs_posts where UserID= 23487 and postlevel <> 1))

Answer 2

你可以试试这个

select ID
from posts
where
    (UserID = 23487 and postlevel <> 1) or
    (EXISTS (select 1 from cs_posts where UserID= 23487 and postlevel <> 1 and ID = ParentID) )

Answer 3

没有必要结合或存在或存在....试试这个：

select distinct F1.id from post F1 inner join
 posts f2 on f2.UserID= 23487 and f2.postlevel <> 1 AND 
(F1.id=f2.id or F1.parentid=f2.id)

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