On Mon, Apr 20, 2020 at 08:31:29PM -0400, Bruce Momjian wrote: > On Mon, Apr 20, 2020 at 04:21:32PM -0400, Tom Lane wrote: > > [ sorry, I'd lost track of this thread ] > > > > Bruce Momjian <br...@momjian.us> writes: > > > I now remember that I wrote the first IS NULL in: > > > CREATE UNIQUE INDEX tests_target_one_null ON tests ((target IS NULL)) > > > WHERE target IS NULL; > > > in hope that if someone is looking for the null value in the column, the > > > IS NULL would allow the index to be used to find it, while 1 or true > > > would not. > > > > Well, that's not the case: > > > > regression=# create index tenk1_null_index on tenk1((1)) where ten is null; > > CREATE INDEX > > regression=# explain select * from tenk1 where ten is null; > > QUERY PLAN > > > > -------------------------------------------------------------------------------- > > Index Scan using tenk1_null_index on tenk1 (cost=0.12..8.14 rows=1 > > width=244) > > (1 row) > > > > (Maybe it was true at some time in the past, but not any more.) > > > > Also, it complicates the example, and since you didn't explain the > > reason for the complication, I think it's pretty confusing. > > > > But really I still don't see the need for these additional examples > > at all. It's especially weird that what you want to do is have > > some examples on that page have <example> markup and others not. > > OK, seems like only you and I care about this issue, which I take to > mean that we should minimize what we are adding here. What the attached > patch does is to remove the previous commit, and just add a sentence to > the last example to mention the ability restrict a column to a single > NULL.
Patch applied. -- Bruce Momjian <br...@momjian.us> https://momjian.us EnterpriseDB https://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
