PHP MySQL左联接没有结果问题

Question

i've a query using left join, my problem is if right table is empty i cant get value which i'm using for ON clause, i mean;

   SELECT members.*,
          photos.* 
   FROM   members LEFT JOIN photos on members.member_id = photos.member_id

now, if it returns a result from photos table, its ok. But when there is no result from photos table, it returns from members table but it does not returns member_id. it returns all others from members table but not member_id

Answer 1

The problem here is that you have two columns with the same name.

Try renaming one to avoid the collision:

SELECT *, members.member_id AS real_member_id

Answer 2

Give the members.member_id an alias name.

SELECT members.member_id as m_id, [other column you want] 
FROM members LEFT JOIN photos on members.member_id = photos.member_id

Answer 3

What do you mean by it returns all others from members table but not member_id ? Is it returning (null) ? Basically yes it all returns all the records from the members table because you are joining it from the left ( members table). But if the record from member_id does not exist, the it returns null . You have to give an ALIAS for that column since you have two fields with the same name.

members.member_id AS MemberID

Answer 4

It's better to expicitedly write which columns you want in the SELECT list:

SELECT members.member_id
       members.name,
       photos.photo_id,
       photos.filename,
       ... 

Then you can be sure that no 2 columns have the same name. It's also better because when one of the table's structure is changed, your query will break and you'll find out easily why. Now it was broken by working in an unexpected way.

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If the only common column is member_id and you really need all the columns, this will work too:

SELECT * 
FROM   members NATURAL LEFT JOIN photos