I have a table with just two columns:
ts::timestamptz (unique),
values::jsonb
I need to find a row with specific ts, but no matter how I cast and convert things around, it just does not work. E.g.
select t.ts::timestamp from table t limit 1 ... returns 2020-03-16 12:46:02
this query
to_timestamp('2020-03-16 12:46:02','YYYY-MM-DD HH24:MI:SS') ... returns 2020-03-16 12:46:02
but query
select * from table t where t.ts::timestamp = to_timestamp('2020-03-16 12:46:02','YYYY-MM-DD HH24:MI:SS')
returns nothing. Now apparently I'm doing a rookie mistake somewhere, but I just can't see it.
Related
how are you?
I needed to store an array of numbers as JSONB in PostgreSQL.
Now I'm trying to calculate stats moments from this JSON, I'm facing some issues.
Sample of my data:
I already was able to convert a JSON into a float array.
I used a function to convert jsonb to float array.
CREATE OR REPLACE FUNCTION jsonb_array_castdouble(jsonb) RETURNS float[] AS $f$
SELECT array_agg(x)::float[] || ARRAY[]::float[] FROM jsonb_array_elements_text($1) t(x);
$f$ LANGUAGE sql IMMUTABLE;
Using this SQL:
with data as (
select
s.id as id,
jsonb_array_castdouble(s.snx_normalized) as serie
FROM
spectra s
)
select * from data;
I found a function that can do these calculations and I need to pass an array for that: https://github.com/ellisonch/PostgreSQL-Stats-Aggregate/
But this function requires an array in another way: unnested
I already tried to use unnest, but it will get only one value, not the entire array :(.
My goal is:
Be able to apply stats moment (kurtosis, skewness) for each row.
like:
index
skewness
1
21.2131
2
1.123
Bonus: There is a way to not use this 'with data', use the transformation in the select statement?
snx_wavelengths is JSON, right? And also you provided it as a picture and not text :( the data looks like (id, snx_wavelengths) - I believe you meant id saying index (not a good idea to use a keyword, would require identifier doublequotes):
1,[1,2,3,4]
2,[373,232,435,84]
If that is right:
select id, (stats_agg(v::float)).skewness
from myMeasures,
lateral json_array_elements_text(snx_wavelengths) v
group by id;
DBFiddle demo
BTW, you don't need "with data" in the original sample if you don't want to use and could replace with a subquery. ie:
select (stats_agg(n)).* from (select unnest(array[16,22,33,24,15])) data(n)
union all
select (stats_agg(n)).* from (select unnest(array[416,622,833,224,215])) data(n);
EDIT: And if you needed other stats too:
select id, "count","min","max","mean","variance","skewness","kurtosis"
from myMeasures,
lateral (select (stats_agg(v::float)).* from json_array_elements_text(snx_wavelengths) v) foo
group by id,"count","min","max","mean","variance","skewness","kurtosis";
DBFiddle demo
I have a big table in a postgres db with location of units. Now I need to retrieve a location for every 60 seconds.
In Mysql, this is a piece of cake: select * from location_table where unit_id = '123' GROUP BY round(timestamp / 60)
But in postgres this seems to be a very hard problem. I also have the timestamps in dateformat rather than in epoch format.
Here is an example of how the table looks
CREATE TABLE location_table (
unit_id int,
"timestamp" timestamp(3) without time zone NOT NULL,
lat double precision,
lng double precision
);
Use date_trunc() to make sets per minute:
SELECT * -- most likely not what you want
FROM location_table
WHERE unit_id = 123 -- numbers don't need quotes '
GROUP BY date_trunc('minute', 'timestamp');
The * is of course wrong, but I don't know what you want to know about the GROUP so I can't come up with something better.
Edit:
When you need a random result from your table, DISTINCT ON () could do the job:
SELECT DISTINCT ON(date_trunc('minute', timestamp))
* -- your columns
FROM location_table;
There are other (standard SQL) solutions as well, like using row_number().
I have been trying to change all the values in a column. When I do it turns out to take my table and drop all the rows that match my criteria in the where clause.
Example
|_Month_|_Cost_|_Title_|
|___2___|_15.99|_hello_|
|___2___|_32.87|_John__|
|___2___|_32.87|_Neat__|
|___3___|_32.87|_Kelps_|
|___4___|_32.87|_Gulp__|
|___5___|_32.87|_Tried_|
I run this Query
UPDATE tableName SET Month = 'FEB' WHERE Month = 2;
The Change:
|_Month_|_Cost_|_Title_|
|__FEB__|_32.87|_Neat__|
|___3___|_32.87|_Kelps_|
|___4___|_32.87|_Gulp__|
|___5___|_32.87|_Tried_|
What I need:
|_Month_|_Cost_|_Title_|
|__FEB__|_15.99|_hello_|
|__FEB__|_32.87|_John__|
|__FEB__|_32.87|_Neat__|
|___3___|_32.87|_Kelps_|
|___4___|_32.87|_Gulp__|
|___5___|_32.87|_Tried_|
Where am I going wrong?
I have also tried to get the date changed from a timestamp with
SELECT TO_DATE(payment_timestamp, 'Mon") payment_month
from tablename;
but PostgreSQL doesn't recognize the TO_DATE()?? Can someone tell me why?
So I have a string time column in a table and now I want to change that time to date time type and then query data for selected dates.
Is there a direct way to do so? One way I could think of is
1) add a new column
2) insert values into it with converted date
3) Query using the new column
Here I am stuck with the 2nd step with INSERT so need help with that
ALTER TABLE "nds".”unacast_sample_august_2018"
ADD COLUMN new_date timestamp
-- Need correction in select statement that I don't understand
INSERT INTO "nds".”unacast_sample_august_2018” (new_date)
(SELECT new_date from_iso8601_date(substr(timestamp,1,10))
Could some one help me with correction and if possible a better way of doing it?
Tried other way to do in single step but gives error as Column does not exist new_date
SELECT *
FROM (SELECT from_iso8601_date(substr(timestamp,1,10)) FROM "db_name"."table_name") AS new_date
WHERE new_date > from_iso8601('2018-08-26') limit 10;
AND
SELECT new_date = (SELECT from_iso8601_date(substr(timestamp,1,10)))
FROM "db_name"."table_name"
WHERE new_date > from_iso8601('2018-08-26') limit 10;
Could someone correct these queries?
You don't need those steps, just use USING CAST clause on your ALTER TABLE:
CREATE TABLE foobar (my_timestamp) AS
VALUES ('2018-09-20 00:00:00');
ALTER TABLE foobar
ALTER COLUMN my_timestamp TYPE timestamp USING CAST(my_timestamp AS TIMESTAMP);
If your string timestamps are in a correct format this should be enough.
Solved as follows:
select *
from
(
SELECT from_iso8601_date(substr(timestamp,1,10)) as day,*
FROM "db"."table"
)
WHERE day > date_parse('2018-08-26', '%Y-%m-%d')
limit 10
I have a problem with the query below in postgres
SELECT u.username,l.description,l.ip,SUBSTRING(l.createdate,0,11) as createdate,l.action
FROM n_logs AS l LEFT JOIN n_users AS u ON u.id = l.userid
WHERE SUBSTRING(l.createdate,0,11) >= '2009-06-07'
AND SUBSTRING(l.createdate,0,11) <= '2009-07-07';
I always used the above query in an older version of postgres and it worked 100%. Now with the new version of posgres it gives me errors like below
**ERROR: function pg_catalog.substring(timestamp without time zone, integer, integer) does not exist
LINE 1: SELECT u.username,l.description,l.ip,SUBSTRING(l.createdate,...
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.**
I assume it has something to do with datatypes, that the data is a time zone and that substring only support string datatypes, now my question is what can I do about my query so that my results would come up?
The explicit solution to your problem is to cast the datetime to string.
...,SUBSTRING(l.createdate::varchar,...
Now, this isn't at all a good practice to use the result to compare dates.
So, the good solution to your need is to change your query using the explicit datetime manipulation, comparison and formatting functions, like extract() and to_char()
You'd have to change your query to have a clause like
l.createdate::DATE >= '2009-06-07'::DATE
AND l.createdate::DATE < '2009-07-08'::DATE;
or one of the alternatives below (which you should really accept instead of this.)
SELECT u.username, l.description, l.ip,
CAST(l.createdate AS DATE) as createdate,
l.action
FROM n_logs AS l
LEFT JOIN
n_users AS u
ON u.id = l.userid
WHERE l.createdate >= '2009-06-07'::TIMESTAMP
AND l.createdate < '2009-07-07'::TIMESTAMP + '1 DAY'::INTERVAL
I'm not sure what you want to achieve, but basically "substring" on date datatypes is not really well defined, as it depends on external format of said data.
In most of the cases you should use extract() or to_char() functions.
Generally - for returning data you want to_char(), and for operations on it (including comparison) - extract(). There are some cases where this general rule does not apply, but these are usually signs of not really well thought data-structure.
Example:
# select to_char( now(), 'YYYY-MM-DD');
to_char
------------
2009-07-07
(1 row)
For extract let's write a simple query that will list all objects created after 8pm:
select * from objects where extract(hour from created) >= 20;
A variation on the Quassnoi's answer:
SELECT
u.username,
l.description,
l.ip,
CAST(l.createdate AS DATE) as createdate,
l.action
FROM
n_logs AS l
LEFT JOIN
n_users AS u
ON
(u.id = l.userid)
WHERE
l.createdate::DATE BETWEEN '2009-06-07'::DATE AND '2009-07-07'::DATE
If you use Postgresql, you will receive:
select('SUBSTRING(offer.date_closed, 0, 11)')
function substr(timestamp without time zone integer integer) does not
exist
Use:
select('SUBSTRING(CONCAT(offer.date_closed, \'\'), 0, 11)')