Re: [HACKERS] lag(bigint,int,int), etc?

On Tue, Jun 27, 2017 at 10:01 AM, Colin 't Hart <colinthart@gmail.com> wrote:
> Hi,
>
> The following rather contrived example illustrates that lag(), lead()
> (and probably other functions) can't automatically cast an integer to
> a bigint:
>
> select lag(sum,1,0) over () from (select sum(generate_series) over
> (order by generate_series) from generate_series(1,10)) x;
> ERROR:  function lag(bigint, integer, integer) does not exist
> LINE 1: select lag(sum,1,0) over () from (select sum(generate_series...
>                ^
> HINT:  No function matches the given name and argument types. You
> might need to add explicit type casts.
>
>
> I guess this is because the lag() and lead() functions take any type,
> and hence the default must be of the same type.
> This had me stumped for a few while until I realised that the types
> were different.
>
> Would there be any way to implement an automatic conversion?
>
> On the off-chance that this is actually a bug, this is on 9.6.3, but
> it also occurs on 9.3.17

Why not cast the arguments?  The first and the third argument have to
be the same, and the second argument is always int.

merlin