Re: BUG #14363: CASE against a literal value produces correct against, same expression against a column null doesn't

On 10/10/16, hcate3(at)gmail(dot)com <hcate3(at)gmail(dot)com> wrote:
> The following bug has been logged on the website:
>
> Bug reference: 14363
> Logged by: Henry Cate
> Email address: hcate3(at)gmail(dot)com
> PostgreSQL version: 9.5.2
> Operating system: x86_64-pc-linux-gnu
> Description:
>
> With this setup:
>
> drop table if exists t2;
> create table t2 (
> order_key int,
> decimal_9_1 decimal(9,1),
> decimal_18_1 decimal(18,1));
>
> insert into t2 values (3, 901.8, null);
>
>
> This query:
>
> select decimal_9_1, decimal_18_1, (
> case decimal_9_1
> when null then 0
> when decimal_9_1 then 1 end),
> case (
> case decimal_9_1
> when null then 0
> when decimal_9_1 then 1 end)
> when 1 then 2
> when 0 then 3
> end,
> case (
> case decimal_9_1
> when decimal_18_1 then 0
> when decimal_9_1 then 1 end)
> when 1 then 2
> when 0 then 3
> end
> from t2 ;
>
>
> produces these results:
>
> decimal_9_1 | decimal_18_1 | case | case | case
> -------------+--------------+------+------+--------
> 901.8 | <null> | 1 | 2 | <null>
> (1 row)
>
>
> I expect the last two columns to both have a value of 2.
>
> The fourth column compares the result of the inner case statement to NULL
> and produces the correct result. The last column compares to a column which
> does have NULL, but some how Postgres gets confused and returns NULL. It
> should also be returning 2.
>
>
>
> Here is the version information:
>
> ybd_test=# select version();
> version
>
> ----------------------------------------------------------------------------
> PostgreSQL 9.5.2 on x86_64-pc-linux-gnu, compiled by clang version
> 3.8.0-2ubuntu3 (tags/RELEASE_380/final), 64-bit
> (1 row)

Upgrade to the newest version of 9.5. It works as expected as of 9.5.4
and 9.6.0:

psql (9.5.4)
Type "help" for help.

postgres=# create table t2 (
postgres(# order_key int,
postgres(# decimal_9_1 decimal(9,1),
postgres(# decimal_18_1 decimal(18,1));
CREATE TABLE
postgres=#
postgres=# insert into t2 values (3, 901.8, null);
INSERT 0 1
postgres=# select decimal_9_1, decimal_18_1, (
postgres(# case decimal_9_1
postgres(# when null then 0
postgres(# when decimal_9_1 then 1 end),
postgres-# case (
postgres(# case decimal_9_1
postgres(# when null then 0
postgres(# when decimal_9_1 then 1 end)
postgres-# when 1 then 2
postgres-# when 0 then 3
postgres-# end,
postgres-# case (
postgres(# case decimal_9_1
postgres(# when decimal_18_1 then 0
postgres(# when decimal_9_1 then 1 end)
postgres-# when 1 then 2
postgres-# when 0 then 3
postgres-# end
postgres-# from t2 ;
decimal_9_1 | decimal_18_1 | case | case | case
-------------+--------------+------+------+------
901.8 | | 1 | 2 | 2
(1 row)

postgres=# select version();
version
----------------------------------------------------------------------------------------------------------
PostgreSQL 9.5.4 on x86_64-pc-linux-gnu, compiled by gcc (Gentoo
4.7.3-r1 p1.4, pie-0.5.5) 4.7.3, 64-bit
(1 row)

--
Best regards,
Vitaly Burovoy