sql server - 连接空值

发布于 2024-11-10 12:56:16 字数 294 浏览 4 评论 0原文

我有两张桌子。一个有链接列表，另一个包含其样式（如果有）。后者是一个稀疏表，即当它们的值为空时，它没有相应的行。我运行以下查询：

select hl.*, hls.colorCode, hls.bold
from HeaderLinks hl, HeaderLinkStyles hls 
where hl.LinkId = hls.linkID
order by row asc, [column] asc

我想修改它，以便如果特定记录不存在行，这些列将在结果集中接收空值。

谢谢你！

原文

I have two tables. One has a list of links and the other one holds thier styles if available.
The later is a sparse table, i.e. it does not have corresponding rows when their values are null.
I run the following query:

select hl.*, hls.colorCode, hls.bold
from HeaderLinks hl, HeaderLinkStyles hls 
where hl.LinkId = hls.linkID
order by row asc, [column] asc

I want to modify this so that if a row does not exist for the specific record, these columns will receive null values in the result set.

Thank you!

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圈圈圆圆圈圈 2024-11-17 12:56:17

左连接

Select hl.*, hls.colorCode, hls.bold 
From HeaderLinks hl
Left Join HeaderLinkStyles hls on hl.LinkId = hls.linkID
order by row asc,[column] ASC

Left Join

Select hl.*, hls.colorCode, hls.bold 
From HeaderLinks hl
Left Join HeaderLinkStyles hls on hl.LinkId = hls.linkID
order by row asc,[column] ASC

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时光磨忆 2024-11-17 12:56:17

要获取不存在记录的 NULL，您需要在表上使用 LEFT OUTER JOIN 或 RIGHT OUTER JOIN.......

Select hl.*, hls.colorCode, hls.bold From HeaderLinks hl
Left Join HeaderLinkStyles hls on hl.LinkId = hls.linkID order by row asc,[column] ASC

在此处输入图像描述

在此处检查连接：Visual SQL连接的表示

To get the NULL for not exist records you need to use either LEFT OUTER JOIN or RIGHT OUTER JOIN on the table.......

Select hl.*, hls.colorCode, hls.bold From HeaderLinks hl
Left Join HeaderLinkStyles hls on hl.LinkId = hls.linkID order by row asc,[column] ASC

enter image description here

Check joins over here : Visual Representation of SQL Joins

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零度℉ 2024-11-17 12:56:17

当未找到匹配项时，left 或 full 连接将用 null 填充行：

select  *
from    HeaderLinks hl
full outer join
        HeaderLinkStyles hls 
on      hl.LinkId = hls.linkID

左连接仅用 null 填充右侧表，右连接仅填充左手表，而全连接则填充两者。有关直观说明，请参阅A Visual Explanation of SQL 连接。

A left or full join will fill a row with null when no match is found:

select  *
from    HeaderLinks hl
full outer join
        HeaderLinkStyles hls 
on      hl.LinkId = hls.linkID

A left join only fills the right hand table with nulls, a right join only the left hand table, and a full join fills both. For a visual illustration see A Visual Explanation of SQL Joins.

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指尖凝香 2024-11-17 12:56:17

您需要使用左外联接

select hl.*, hls.colorCode, hls.bold
from HeaderLinks hl
    left join HeaderLinkStyles hls on
      hl.LinkId = hls.linkID  
order by row asc, [column] asc

使用外联接

You need to use left outer join

select hl.*, hls.colorCode, hls.bold
from HeaderLinks hl
    left join HeaderLinkStyles hls on
      hl.LinkId = hls.linkID  
order by row asc, [column] asc

Using Outer Joins

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白馒头 2024-11-17 12:56:17

您需要使用 LEFT JOIN

Select 
  hl.*, 
  hls.colorCode, 
  hls.bold 
from 
  HeaderLinks hl 
LEFT JOIN 
  HeaderLinkStyles hls on hl.LinkId = hls.linkID
order by 
  row asc,[column] ASC

You need to use LEFT JOIN

Select 
  hl.*, 
  hls.colorCode, 
  hls.bold 
from 
  HeaderLinks hl 
LEFT JOIN 
  HeaderLinkStyles hls on hl.LinkId = hls.linkID
order by 
  row asc,[column] ASC

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