防止重复的行 [英] prevent duplicate rows

问题描述

你好亲爱的



我有一个带两张桌子的数据库（record_table，附件）



< b> record_table

 ID，subject，note 

附件

<前lang =text> ID，ID_record_table，路径

表之间的关系：

 record_table.id = attachment.ID_record_table 

但是当record_table中的一行有2个附件时。当我使用select语句时，我会在record_table中看到同一行的2个结果。所以如何防止重复行。

（ SELECT  * < span class =code-keyword> FROM  record_table  LEFT   JOIN  attachment   record_table.id = attachment.ID_record_table）

解决方案

因为你加入了这两个在结果集中，您将获得多少行，以满足连接条件的行数。换句话说，如果一个记录有两个附件，则返回两行.-



这些行不是重复的。如果您查看来自附件表的列，您会看到包含两行中的值。



看看 SQL连接的可视化表示 [ ^ ]

试试这个，



sql - 加入两个表并显示全部记录 - 堆栈溢出 [ ^ ]

hello dears

I have one database with two tables (record_table,attachments)

record_table

ID, subject,note

attachments

ID, ID_record_table,path

relationship between tables:

the record_table.id = attachment.ID_record_table

but when one row in record_table has 2 attachment .and when I use select statement i will see 2 results for the same row in record_table. so how can I prevent duplicate rows.

(SELECT * FROM record_table LEFT JOIN attachment on record_table.id = attachment.ID_record_table)

解决方案

Since you're joining the two tables you will get as many rows in the result set how many rows satisfy the join condition. In other words, if one record has two attachments, two rows are returned.-

The rows aren't duplicates. If you have a look at the columns coming from attachment table you see that the contain the values from both rows.

Have a look at Visual Representation of SQL Joins[^]

try this,

sql - join two tables and show all records - Stack Overflow[^]

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