Why I get division by zero for PostgreSQL v13? I suppose rows should be filtered out

Running same query on different versions of PostgreSQL gives different result.

WITH t(a, b) AS (VALUES (1, 0))
SELECT a / b
  FROM t
 WHERE b <> 0;

On v11.10 I get no rows as expected fiddle
On v13.1 I get ERROR: division by zero fiddle

Why I get division by zero for PostgreSQL v13.1? I suppose rows should be filtered out as it done for v11.10

UPD
I think when we join, optimizer should not call lateral function sometimes (when it may) and save time: fiddle

Answer

It looks the order of evaluation is not what one would expect it to be: that is, one would expect that 0 denominators would be filtered out by the where clause before the computation in the select clause happens. Obviously the database chooses to do things differently.

You can, however, easily work around this with nullif():

with t(a, b) as (values (1, 0))
select a / nullif(b, 0)
from t
where b <> 0;

This properly produce no rows.

I would tend qualifying this as a bug, or at least a regression. Playing around in db<>fiddle, your original code works fine in versions 9.4, 9.5, 9.6, 10 and 11, but fails in versions 12 and 13.