INNER JOIN same table - mysql

Question

I am trying to get some rows from the same table. It's a user table: user has user_id and user_parent_id.
I need to get the user_id row and user_parent_id row. I have coded something like this:
SELECT user.user_fname, user.user_lname
FROM users as user
INNER JOIN users AS parent
ON parent.user_parent_id = user.user_id
WHERE user.user_id = $_GET[id]
But it doesn't show the results. I want to display user record and its parent record.

Answer 1

I think the problem is in your JOIN condition.
SELECT user.user_fname,
user.user_lname,
parent.user_fname,
parent.user_lname
FROM users AS user
JOIN users AS parent
ON parent.user_id = user.user_parent_id
WHERE user.user_id = $_GET[id]
Edit:
You should probably use LEFT JOIN if there are users with no parents.

Answer 2

You can also use UNION like
SELECT user_fname ,
user_lname
FROM users
WHERE user_id = $_GET[id]
UNION
SELECT user_fname ,
user_lname
FROM users
WHERE user_parent_id = $_GET[id]

Answer 3

Perhaps this should be the select (if I understand the question correctly)
select user.user_fname, user.user_lname, parent.user_fname, parent.user_lname
... As before

Answer 4

Your query should work fine, but you have to use the alias parent to show the values of the parent table like this:
select
CONCAT(user.user_fname, ' ', user.user_lname) AS 'User Name',
CONCAT(parent.user_fname, ' ', parent.user_lname) AS 'Parent Name'
from users as user
inner join users as parent on parent.user_parent_id = user.user_id
where user.user_id = $_GET[id];

Answer 5

I don't know how the table is created but try this...
SELECT users1.user_id, users2.user_parent_id
FROM users AS users1
INNER JOIN users AS users2
ON users1.id = users2.id
WHERE users1.user_id = users2.user_parent_id

Answer 6

Lets try to answer this question, with a good and simple scenario, with 3 MySQL tables i.e. datetable, colortable and jointable.
first see values of table datetable with primary key assigned to column dateid:
mysql> select * from datetable;
+--------+------------+
| dateid | datevalue |
+--------+------------+
| 101 | 2015-01-01 |
| 102 | 2015-05-01 |
| 103 | 2016-01-01 |
+--------+------------+
3 rows in set (0.00 sec)
now move to our second table values colortable with primary key assigned to column colorid:
mysql> select * from colortable;
+---------+------------+
| colorid | colorvalue |
+---------+------------+
| 11 | blue |
| 12 | yellow |
+---------+------------+
2 rows in set (0.00 sec)
and our final third table jointable have no primary keys and values are:
mysql> select * from jointable;
+--------+---------+
| dateid | colorid |
+--------+---------+
| 101 | 11 |
| 102 | 12 |
| 101 | 12 |
+--------+---------+
3 rows in set (0.00 sec)
Now our condition is to find the dateid's, which have both color values blue and yellow.
So, our query is:
mysql> SELECT t1.dateid FROM jointable AS t1 INNER JOIN jointable t2
-> ON t1.dateid = t2.dateid
-> WHERE
-> (t1.colorid IN (SELECT colorid FROM colortable WHERE colorvalue = 'blue'))
-> AND
-> (t2.colorid IN (SELECT colorid FROM colortable WHERE colorvalue = 'yellow'));
+--------+
| dateid |
+--------+
| 101 |
+--------+
1 row in set (0.00 sec)
Hope, this would help many one.