Home > mailing lists

Thread: Passing a dynamic interval to generate_series()

Passing a dynamic interval to generate_series()

From

Igal Sapir

Date:

01 July, 01:39:26

Hello,

I am trying to pass a dynamic interval to generate_series() with date range.

This works as expected, and generates a series with an interval of 1 month:

SELECT generate_series(
date_trunc('month', current_date),
date_trunc('month', current_date + interval '7 month'),
interval '1 month'

)

This works as expected and returns an interval of 1 month:

SELECT ('1 ' || 'month')::interval;

But this throws an error (SQL Error [42601]: ERROR: syntax error at or near "'1 '"):

SELECT generate_series(
date_trunc('month', current_date),
date_trunc('month', current_date + interval '7 month'),
interval ('1 ' || 'month')::interval
)

And this returns a series with interval of 1 second??

SELECT generate_series(
date_trunc('month', current_date),
date_trunc('month', current_date + interval '7 month'),
(interval '1 ' || 'month')::interval
)

Because this returns an interval of 1 second:

SELECT (interval '1 ' || 'month')::interval;

Is that a bug?

I am able to work around the issue using a CASE statement, but shouldn't it work simply by concatenating the string with the || operator?

Thank you,

Igal

Re: Passing a dynamic interval to generate_series()

From

Tom Lane

Date:

01 July, 01:51:14

Igal Sapir <igal@lucee.org> writes:
> But this throws an error (SQL Error [42601]: ERROR: syntax error at or near
> "'1 '"):

> SELECT generate_series(
>     date_trunc('month', current_date),
>     date_trunc('month', current_date + interval '7 month'),
>     interval ('1 ' || 'month')::interval
> )

You're overthinking it.

SELECT generate_series(
    date_trunc('month', current_date),
    date_trunc('month', current_date + interval '7 month'),
    ('1 ' || 'month')::interval
);
    generate_series
------------------------
 2024-06-01 00:00:00-04
 2024-07-01 00:00:00-04
 2024-08-01 00:00:00-04
 2024-09-01 00:00:00-04
 2024-10-01 00:00:00-04
 2024-11-01 00:00:00-04
 2024-12-01 00:00:00-05
 2025-01-01 00:00:00-05
(8 rows)

It might help to read this:

https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-CONSTANTS-GENERIC

and to experiment with what you get from the constituent elements
of what you tried, rather than trying to guess what they are from
generate_series's behavior.  For example,

select (interval '1 ');
 interval
----------
 00:00:01
(1 row)

select (interval '1 ' || 'month');
   ?column?
---------------
 00:00:01month
(1 row)

            regards, tom lane

Re: Passing a dynamic interval to generate_series()

From

Igal Sapir

Date:

01 July, 02:17:31

On Sun, Jun 30, 2024 at 3:51 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

Igal Sapir <igal@lucee.org> writes:
> But this throws an error (SQL Error [42601]: ERROR: syntax error at or near
> "'1 '"):

> SELECT generate_series(
> date_trunc('month', current_date),
> date_trunc('month', current_date + interval '7 month'),
> interval ('1 ' || 'month')::interval
> )

You're overthinking it.

SELECT generate_series(
date_trunc('month', current_date),
date_trunc('month', current_date + interval '7 month'),
('1 ' || 'month')::interval
);
generate_series
------------------------
2024-06-01 00:00:00-04
2024-07-01 00:00:00-04
2024-08-01 00:00:00-04
2024-09-01 00:00:00-04
2024-10-01 00:00:00-04
2024-11-01 00:00:00-04
2024-12-01 00:00:00-05
2025-01-01 00:00:00-05
(8 rows)

Thank you, Tom. I thought that I tried that too, but apparently I did not because it works the way you wrote it.

It might help to read this:

https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-CONSTANTS-GENERIC

and to experiment with what you get from the constituent elements
of what you tried, rather than trying to guess what they are from
generate_series's behavior. For example,

select (interval '1 ');
interval
----------
00:00:01
(1 row)

select (interval '1 ' || 'month');
?column?
---------------
00:00:01month
(1 row)

I actually did test the expression that I posted, but it might be casting it twice. While your examples that you wrote show 1 month correctly:

SELECT (interval '1 ' || 'month');

?column? |
-------------+
00:00:01month|

SELECT ('1 ' || 'month')::interval;

interval|
--------+
1 mon|

When the expression includes the "::interval" suffix as in the example that I posted it returns 1 second, possibly because it is casting to interval twice (at least on PostgreSQL 16.2 (Debian 16.2-1.pgdg120+2)):

SELECT (interval '1 ' || 'month')::interval;

interval|
--------+
00:00:01|

Anyway, you solved my issue, so thank you very much as always,

Igal

regards, tom lane

Re: Passing a dynamic interval to generate_series()

From

Francisco Olarte

Date:

01 July, 10:20:11

Hi Igal:

On Mon, 1 Jul 2024 at 01:17, Igal Sapir <igal@lucee.org> wrote:

> I actually did test the expression that I posted, but it might be casting it twice.  While your examples that you
wroteshow 1 month correctly:

> SELECT (interval '1 ' || 'month');
> ?column?     |
> -------------+
> 00:00:01month|

No, it does not, try it like this:
s=> with a(x) as ( SELECT (interval '1 ' || 'month')) select x,
pg_typeof(x) from a;
       x       | pg_typeof
---------------+-----------
 00:00:01month | text
(1 row)

And you'll understand what is happening. Cast to interval has higher
priority then concatenation, so you are selecting a 1 second interval,
casting it to text, '00:00:01', adding 'month' at end.

This can also be noticed because month output would not use ':' and have spaces:
s=> with a(x) as ( SELECT '001.00MONTHS'::interval) select x,
pg_typeof(x) from a;
   x   | pg_typeof
-------+-----------
 1 mon | interval
(1 row)

( I used fractions, uppercase and no spaces on input to show how
interval output normalizes ).

Francisco Olarte.

Re: Passing a dynamic interval to generate_series()

From

Shammat

Date:

01 July, 10:37:24

Igal Sapir schrieb am 01.07.2024 um 00:39:
> I am trying to pass a dynamic interval to generate_series() with date range.
>
> This works as expected, and generates a series with an interval of 1 month:
>
> SELECT generate_series(
>     date_trunc('month', current_date),
>     date_trunc('month', current_date + interval '7 month'),
>     interval '1 month'
> )
>
>
> This works as expected and returns an interval of 1 month:
>
> SELECT ('1 ' || 'month')::interval;
>
>
> But this throws an error (SQL Error [42601]: ERROR: syntax error at or near "'1 '"):
>
> SELECT generate_series(
>     date_trunc('month', current_date),
>     date_trunc('month', current_date + interval '7 month'),
>     interval ('1 ' || 'month')::interval
> )

I am a fan of make_interval() when it comes to creating intervals from dynamic parameters:

SELECT generate_series(
    date_trunc('month', current_date),
    date_trunc('month', current_date + interval '7 month'),
    make_interval(months => 1)
)


The value for make_interval() can e.g. passed as a parameter from your programming language.