How can i query table within table? - mysql

Question

How can i make a query that takes everything from one table then joins another table and put the values from the second table in a certain column in the result
What i am asking can be better explained:
clients:
id | name | age | ...
---------------------
15 | something | 30 |
17 | somethiaa | 30 |
13 | ggggthing | 30 |
clients_meta:
id | client_id | meta_key | meta_value |
-----------------------------------------
1 | 15 | location | NY |
2 | 15 | height | 195 |
3 | 15 | job | student |
4 | 13 | location | TN |
This is my current query:
SELECT
`clients`.*,
`clients_meta`.*
FROM `clients`
JOIN clients_meta ON ( clients_meta.client_id = clients.id )
WHERE
`clients_age` = '30'
how can instead of a ugly table like that:
15 | something | 30 | 1 | 15 | location | NY |
15 | something | 30 | 2 | 15 | height | 195 |
15 | something | 30 | 3 | 15 | job | student |
change it to something like:
15 | something | 30 | 1 | 15 | location | NY |
| 2 | 15 | height | 195 |
| 3 | 15 | job | student |
thanks

Answer 1

You can use a variable to check whether the last id is equal to the current id, and in that case output null or '' instead.
select
case when c.ClientId <> #clientid then c.Name else '' end as ClientName,
case when c.ClientId <> #clientid then #ClientId := c.ClientId else '' end as ClientId,
p.ContactId,
p.Name as ContactName
from
Clients c
inner join Contacts p on p.ClientId = c.Clientid
, (select #clientid := -1) x
order by
c.ClientId, p.ContactId
Example: http://sqlfiddle.com/#!2/658e4c/6
Note, this is a bit hacky. I deliberately made ClientId the second field, so I could change and return the clientId variable in the same field. In other, more elaborate cases, you may have to do that in a separate field. But to eliminate that placeholder field from the result, you'll have to embed the whole query in a subselect, and define the wanted fields in the right order on the top level query.

Answer 2

You could choose one value in clients_meta.meta_key to always be first like 'location'. Then you can sort by clients.id, then by whether or not meta_key = 'location'. Any rows where meta_key != 'location', you can hide, like this:
select
case when clients_meta.meta_key = 'location'
then clients.id else '' end as id
, case when clients_meta.meta_key = 'location'
then clients.name else '' end as name
, case when clients_meta.meta_key = 'location'
then clients.age else '' end as age
, clients_meta.*
from clients join clients_meta on (clients_meta.client_id = clients.id)
where clients.age = '30'
order by clients.id, clients_meta.meta_key = 'location' desc;
You will obtain the results that you wanted:
+------+-----------+------+----+-----------+----------+------------+
| id | name | age | id | client_id | meta_key | meta_value |
+------+-----------+------+----+-----------+----------+------------+
| 13 | ggggthing | 30 | 4 | 13 | location | TN |
| 15 | something | 30 | 1 | 15 | location | NY |
| | | | 3 | 15 | job | student |
| | | | 2 | 15 | height | 195 |
+------+-----------+------+----+-----------+----------+------------+