MySQL，使用一个查询的值从另一个查询获取结果

Question

I am an absolute newbie with MySQL and other than basic select functions I don't know much more! I have been reading various posts about joining Queries etc But it's currently going over my head far too much to be able to build what I need and I'm short of time to learn!

So would anyone be able to pull me together a query to work out the below, please?

I have 3 tables which contain fields below that I need to use.

Accounts

i_account,
id,
i_env (this value would be =2),
first_usage_time

UA

i_ua,
mac,
inventory_id,
description

UA_Links

i_ua,
i_account

So as you can see the table UA_Links contains the two fields that tie the UA and Accounts tables together.

What I need to do is, output from the Accounts table, id and first_usage along with the mac, inventory_id and description from the UA table.

Hopefully that makes sense?

Many thanks in advance Mike

Answer 1

The most simple way of doing this is to create a simple join.

SELECT Account.id, Accounts.first_usage_time, UA.mac, UA.inventory_id, UA.description 
FROM Accounts, UA, UA_Links
WHERE Accounts.id = UA_Links.i_account 
AND UA.i_ua = UA_Links.i_ua

A little explanation: you can use a comma to select multiple tables. If you want to select a column you need to use the syntax {tablename}.{column_name}. To connect the 3 tables together you need to link the ID's in the WHERE statement.

I'm not totally sure if I got the correct columns, you might want to check that (are UA.i_ua and UA_Links.i_ua the same?).

Answer 2

May be this is can help..:)

select a.id,a.first_usage_time
from Accounts a
left join UA_Links b
on b.i_account=a.i_account
left join UA c
on c.i_ua=b.i_ua

Answer 3

This is a very simple join, all you need is to tell the query which field matches which of the other table:

select * from accounts as a inner join ua_links as l 
on a.i_account = l.i_account 
Inner join ua on l.i_ua = ua.i_ua

Answer 4

Hope this will work for your needs,

select acc.id as YOURALIAS, acc.first_usage_time as YOURALIAS, 
ua.mac as YOURALIAS, ua.inventory_id as YOURALIAS, 
ua.description as YOURALIAS 
from ua INNER JOIN ua_links ON ua.i_ua = ua_links.i_ua 
inner join accounts acc on ua_links.i_account = acc.i_account

It is a best practice to use aliases, you can find more on http://www.w3schools.com/sql/sql_alias.asp .