generate_series function in Amazon Redshift

问题

I tried the below:

SELECT * FROM generate_series(2,4);
generate_series
-----------------
           2
           3
           4
(3 rows)

SELECT * FROM generate_series(5,1,-2);                                                             
generate_series
-----------------
           5
           3
           1
(3 rows)

But when I try,

select * from generate_series('2011-12-31'::timestamp, '2012-12-31'::timestamp, '1 day');

It generated error.

ERROR:  function generate_series(timestamp without time zone, timestamp without time zone, "unknown") does not exist
HINT:  No function matches the given name and argument types. You may need to add explicit type casts.

I use PostgreSQL 8.0.2 on Redshift 1.0.757.
Any idea why it happens?

UPDATE:

generate_series is working with Redshift now.

SELECT CURRENT_DATE::TIMESTAMP  - (i * interval '1 day') as date_datetime 
FROM generate_series(1,31) i 
ORDER BY 1

This will generate last 30 days date

回答1:

The version of generate_series() that supports dates and timestamps was added in Postgres 8.4.

As Redshift is based on Postgres 8.0, you need to use a different way:

select timestamp '2011-12-31 00:00:00' + (i * interval '1 day')
from  generate_series(1, (date '2012-12-31' - date '2011-12-31')) i;

If you "only" need dates, this can be abbreviated to:

select date '2011-12-31' + i
from  generate_series(1, (date '2012-12-31' - date '2011-12-31')) i;

回答2:

generate_series is working with Redshift now.

SELECT CURRENT_DATE::TIMESTAMP  - (i * interval '1 day') as date_datetime 
FROM generate_series(1,31) i 
ORDER BY 1

This will generate last 30 days date

回答3:

There is no generate_series() function in Redshift for Date Range but you can generate the series with below steps...

Step 1: Created a table genid and insert constant value as 1 for number of times you need to generate the series. If you need the series to be generated for 12 month you can insert 12 times. Better you can insert for more number of times like 100, so that you do not face any issue.

create table genid(id int)

------------ for number of months insert into genid values(1)

Step 2: The table for which you need to generate the series.

create table pat(patid varchar(10),stdt timestamp, enddt timestamp);

insert into pat values('Pat01','2018-03-30 00:00:00.0','2018-04-30 00:00:00.0')

insert into pat values('Pat02','2018-02-28 00:00:00.0','2018-04-30 00:00:00.0')

insert into pat values('Pat03','2017-10-28 00:00:00.0','2018-04-30 00:00:00.0')

Step 3: This query will generate the series for you.

with cte as 
(
select max(enddt) as maxdt
from pat
) ,
cte2 as(
select dateadd('month', -1 * row_number() over(order by 1),  maxdt::date ) as gendt  
from  genid , cte
) select * 
from pat, cte2
where gendt between stdt and enddt

回答4:

I found a solution here for my problem of not being able to generate a time dimension table on Redshift using generate_series(). You can generate a temporary sequence by using the following SQL snippet.

with digit as (
    select 0 as d union all 
    select 1 union all select 2 union all select 3 union all
    select 4 union all select 5 union all select 6 union all
    select 7 union all select 8 union all select 9        
),
seq as (
    select a.d + (10 * b.d) + (100 * c.d) + (1000 * d.d) as num
    from digit a
        cross join
        digit b
        cross join
        digit c
        cross join
        digit d
    order by 1        
)
select (getdate()::date - seq.num)::date as "Date"
from seq;

The generate_series() function, it seems, is not supported completely on Redshift yet. If I run the SQL mentioned in the answer by DJo, it works, because the SQL runs only on the leader node. If I prepend insert into dim_time to the same SQL it doesn't work.

来源：https://stackoverflow.com/questions/22554398/generate-series-function-in-amazon-redshift

标签

amazon-redshift

generate-series