Mark Stosberg wrote: > > > >Here's a situation I've run into more than once with SQL: > >I want to select all the rows
ina table that match a criteria, where one >of the criteria is possibly having a related entry in a second table. For
>myexample, lets say I have table named 'messages' and another named >'message_attachments'. The former has a primary
keyof msg_id, the latter >also contains msg_id, and has an attachment_id as it's primary key. > >This statement shows
meall the messages that also have attachments: > >SELECT > messages.msg_id, > message_attachments.attachment_id >
FROM messages,message_attachments > WHERE messages.msg_id = message_attachments.msg_id; > >But I want a statement
thatsays: "Show me all the messages, and include >information about an attachment if they have one"
SELECT m.msg_id, a.attachment_id FROM messages AS m LEFT OUTER JOIN message-attachments AS a ON m.msg_id =
a.msg_id;
This requires 7.1 for the LEFT OUTER JOIN. In 7.0.3 you could do it
with a UNION.
--
Oliver Elphick Oliver.Elphick@lfix.co.uk
Isle of Wight http://www.lfix.co.uk/oliver
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