Generate random values from table - postgresql

Question

I'd like to generate random values in order to fill a table.
First, I have a city_table :
CREATE TABLE t_city_ci (
ci_id SERIAL PRIMARY KEY,
ci_name VARCHAR(100) NOT NULL
);
So I insert random values like this :
INSERT INTO t_city_ci ("ci_name")
SELECT DISTINCT(d.str)
FROM (
SELECT
(
SELECT string_agg(x, '') as str
FROM (
SELECT chr(ascii('A') + (random() * 25)::integer)
-- reference 'b' so it is correlated and re-evaluated
FROM generate_series(1, 10 + b * 0)
) AS y(x)
)
FROM generate_series(1,10000) as a(b)) as d;
Now, I have a temperature table that looks like this :
CREATE TABLE dw_core.t_temperatures_te (
te_id SERIAL PRIMARY KEY,
ci_id INTEGER,
te_temperature FLOAT NOT NULL,
te_date TIMESTAMP NOT NULL DEFAULT NOW()
);
How can I fill a temperature table with :
Random date from last year
Random temperature between -30 and 50
Random values from t_city table ?
I tried this but the date never changes :
INSERT INTO dw_core.t_temperatures_te ("ci_id","te_temperature","te_date")
SELECT *
FROM (
SELECT (random() * (SELECT MAX(ci_id) FROM dw_core.t_city_ci) + 1)::integer
-- reference 'b' so it is correlated and re-evaluated
FROM generate_series(1, 100000 )
) AS y
,(select random() * -60 + 45 FROM generate_series(1,1005)) d(f),
(select timestamp '2014-01-10 20:00:00' +
random() * (timestamp '2014-01-20 20:00:00' -
timestamp '2016-01-10 10:00:00')) dza(b)
LIMIT 1000000;
Thanks a lot

Answer 1

Something like this?
select * from (
select
(random() * 100000)::integer as ci_id,
-30 + (random() * 80) as temp,
'2014-01-01'::date + (random() * 365 * '1 day'::interval) as time_2014
from generate_series(1,1000000) s
) foo
inner join t_city_ci c on c.ci_id = foo.ci_id;
Here's a sample of the generated data:
select
(random() * 100000)::integer as ci_id,
-30 + (random() * 80) as temp,
'2014-01-01'::date + (random() * 365 * '1 day'::interval) as time_2014
from generate_series(1,10);
ci_id | temp | time_2014
-------+-------------------+----------------------------
84742 | 31.6278865475337 | 2014-10-16 21:36:45.371176
16390 | 10.665458049935 | 2014-11-13 19:59:54.148177
87067 | 43.2082599369847 | 2014-06-01 16:14:43.021094
25718 | -7.78245567240867 | 2014-07-23 05:53:10.036914
99538 | -5.82924078024423 | 2014-06-08 06:44:02.081918
71720 | 22.3102275898262 | 2014-06-15 08:24:00.327841
24740 | 4.65809369210996 | 2014-05-19 02:20:58.804213
56861 | -20.750980894431 | 2014-10-01 06:09:54.117367
47929 | -24.4018202994027 | 2014-11-24 13:39:54.096337
30772 | 46.7239395141247 | 2014-08-27 04:50:46.785239
(10 rows)