INNER JOIN same table

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

Answer 1

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.