On 2/24/07, Sumeet <[EMAIL PROTECTED]> wrote:
Hi all,
I'm trying to write a query to select random values from a set of 'GROUP
BY'
....see the scenario below to understand the problem here (the actual
problem cannot be discussed here so i'm taking an example scenario)
Assume there is a table
id | name | year_of_birth
query: I want to select for each year_of_birth a random name.
Dear Sumeet
postgresql DISTINCT ON may be of help , but its not standard sql.
regds
mallah.
tradein_clients=> SELECT * from temp.test;
+----+------+-----+
| id | name | yob |
+----+------+-----+
| 1 | A | 2 |
| 2 | B | 2 |
| 3 | C | 2 |
| 4 | D | 1 |
| 5 | E | 1 |
| 6 | F | 1 |
+----+------+-----+
(6 rows)
tradein_clients=> SELECT distinct on (yob) id,name,yob from temp.test order
by yob,random();
+----+------+-----+
| id | name | yob |
+----+------+-----+
| 5 | E | 1 |
| 1 | A | 2 |
+----+------+-----+
(2 rows)
tradein_clients=> SELECT distinct on (yob) id,name,yob from temp.test order
by yob,random();
+----+------+-----+
| id | name | yob |
+----+------+-----+
| 4 | D | 1 |
| 1 | A | 2 |
+----+------+-----+
(2 rows)
--> so i do a group by year_of_birth, now i have a set of names, is there
any function to select just one name from these set of names.
The current approach i'm using to solve this problem is
1) getting these names in a single string using a custom function
'group_concat'
2) Convert the single string into an array
3) use postgresql random function to generate a random number
4) us the random number to select a element from the array previously
created.
The solution is there but it's kinda hack, is there any other better way
of
solving this problem.
Thanks,
Sumeet
