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* unique index with several columns
@ 2022-03-04 15:06 Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
0 siblings, 2 replies; 12+ messages in thread
From: Voillequin, Jean-Marc @ 2022-03-04 15:06 UTC (permalink / raw)
To: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Hello,
On PG:
RRT=> create table t(c1 char, c2 char);
ERROR: relation "t" already exists
RRT=> create unique index idx on t(c1,c2);
ERROR: relation "idx" already exists
RRT=> insert into t(c1,c2) values (null,null);
INSERT 0 1
RRT=> insert into t(c1,c2) values (null,null);
INSERT 0 1
RRT=> insert into t(c1,c2) values ('a',null);
INSERT 0 1
RRT=> insert into t(c1,c2) values ('a',null);
INSERT 0 1
On Oracle:
SQL> create table t(c1 char, c2 char);
Table created.
SQL> create unique index idx on t(c1,c2);
Index created.
SQL> insert into t(c1,c2) values (null,null);
1 row created.
SQL> insert into t(c1,c2) values (null,null);
1 row created.
SQL> insert into t(c1,c2) values ('a',null);
1 row created.
SQL> insert into t(c1,c2) values ('a',null);
insert into t(c1,c2) values ('a',null)
*
ERROR at line 1:
ORA-00001: unique constraint (RRT.IDX) violated
When one of the field is null, PG considers that the tuple is not the same:
('a',null) is not equal to ('a',null)
So, the unique constraint is not violated in PG.
But is there a way to have the same feature than Oracle?
I already tried with:
create unique index idx on t(coalesce(c1,''),coalesce(c2,''))
But in this case, I cannot insert several (null,null) without raising a duplicate key error.
Thanks & regards
-----------------------------------------
Moody's monitors email communications through its networks for regulatory compliance purposes and to protect its customers, employees and business and where allowed to do so by applicable law. The information contained in this e-mail message, and any attachment thereto, is confidential and may not be disclosed without our express permission. If you are not the intended recipient or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution or copying of this message, or any attachment thereto, in whole or in part, is strictly prohibited. If you have received this message in error, please immediately notify us by telephone, fax or e-mail and delete the message and all of its attachments. Every effort is made to keep our network free from viruses. You should, however, review this e-mail message, as well as any attachment thereto, for viruses. We take no responsibility and have no liability for any computer virus which may be transferred via this e-mail message.
-----------------------------------------
^ permalink raw reply [nested|flat] 12+ messages in thread
* RE: unique index with several columns
@ 2022-03-04 15:09 Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
parent: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
1 sibling, 0 replies; 12+ messages in thread
From: Voillequin, Jean-Marc @ 2022-03-04 15:09 UTC (permalink / raw)
To: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Sorry, the test case is:
On PG:
RRT=> create table t(c1 char, c2 char);
CREATE TABLE
RRT=> create unique index idx on t(c1,c2);
CREATE INDEX
RRT=> insert into t(c1,c2) values (null,null);
INSERT 0 1
RRT=> insert into t(c1,c2) values (null,null);
INSERT 0 1
RRT=> insert into t(c1,c2) values ('a',null);
INSERT 0 1
RRT=> insert into t(c1,c2) values ('a',null);
INSERT 0 1
On Oracle:
SQL> create table t(c1 char, c2 char);
Table created.
SQL> create unique index idx on t(c1,c2);
Index created.
SQL> insert into t(c1,c2) values (null,null);
1 row created.
SQL> insert into t(c1,c2) values (null,null);
1 row created.
SQL> insert into t(c1,c2) values ('a',null);
1 row created.
SQL> insert into t(c1,c2) values ('a',null);
insert into t(c1,c2) values ('a',null)
*
ERROR at line 1:
ORA-00001: unique constraint (RRT.IDX) violated
The question is the same.
From: Voillequin, Jean-Marc
Sent: Friday, March 4, 2022 4:07 PM
To: pgsql-sql@lists.postgresql.org
Subject: unique index with several columns
Hello,
On PG:
RRT=> create table t(c1 char, c2 char);
ERROR: relation "t" already exists
RRT=> create unique index idx on t(c1,c2);
ERROR: relation "idx" already exists
RRT=> insert into t(c1,c2) values (null,null);
INSERT 0 1
RRT=> insert into t(c1,c2) values (null,null);
INSERT 0 1
RRT=> insert into t(c1,c2) values ('a',null);
INSERT 0 1
RRT=> insert into t(c1,c2) values ('a',null);
INSERT 0 1
On Oracle:
SQL> create table t(c1 char, c2 char);
Table created.
SQL> create unique index idx on t(c1,c2);
Index created.
SQL> insert into t(c1,c2) values (null,null);
1 row created.
SQL> insert into t(c1,c2) values (null,null);
1 row created.
SQL> insert into t(c1,c2) values ('a',null);
1 row created.
SQL> insert into t(c1,c2) values ('a',null);
insert into t(c1,c2) values ('a',null)
*
ERROR at line 1:
ORA-00001: unique constraint (RRT.IDX) violated
When one of the field is null, PG considers that the tuple is not the same:
('a',null) is not equal to ('a',null)
So, the unique constraint is not violated in PG.
But is there a way to have the same feature than Oracle?
I already tried with:
create unique index idx on t(coalesce(c1,''),coalesce(c2,''))
But in this case, I cannot insert several (null,null) without raising a duplicate key error.
Thanks & regards
-----------------------------------------
Moody's monitors email communications through its networks for regulatory compliance purposes and to protect its customers, employees and business and where allowed to do so by applicable law. The information contained in this e-mail message, and any attachment thereto, is confidential and may not be disclosed without our express permission. If you are not the intended recipient or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution or copying of this message, or any attachment thereto, in whole or in part, is strictly prohibited. If you have received this message in error, please immediately notify us by telephone, fax or e-mail and delete the message and all of its attachments. Every effort is made to keep our network free from viruses. You should, however, review this e-mail message, as well as any attachment thereto, for viruses. We take no responsibility and have no liability for any computer virus which may be transferred via this e-mail message.
-----------------------------------------
^ permalink raw reply [nested|flat] 12+ messages in thread
* Re: unique index with several columns
@ 2022-03-04 15:32 David G. Johnston <david.g.johnston@gmail.com>
parent: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
1 sibling, 1 reply; 12+ messages in thread
From: David G. Johnston @ 2022-03-04 15:32 UTC (permalink / raw)
To: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; +Cc: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
On Fri, Mar 4, 2022 at 8:07 AM Voillequin, Jean-Marc <
Jean-Marc.Voillequin@moodys.com> wrote:
>
>
> When one of the field is null, PG considers that the tuple is not the same:
>
> ('a',null) is not equal to ('a',null)
>
> So, the unique constraint is not violated in PG.
>
>
>
> But is there a way to have the same feature than Oracle?
>
>
>
> I already tried with:
>
> create unique index idx on t(coalesce(c1,''),coalesce(c2,''))
>
>
>
> But in this case, I cannot insert several (null,null) without raising a
> duplicate key error.
>
>
>
You just said you wanted nulls to be considered equal to each other...
Not tested but these should work in conjunction with each other:
CREATE UNIQUE INDEX idx ON t (c1, c2) WHERE c1 IS NOT NULL AND c2 IS NOT
NULL;
CREATE UNIQUE INDEX idx2 ON t (c1) WHERE c2 IS NULL AND c1 IS NOT NULL;
CREATE UNIQUE INDEX idx3 ON t (c2) WHERE c1 IS NULL AND c2 IS NOT NULL;
--CREATE INDEX idx4 ON t (c1, c2) WHERE c1 IS NULL AND c2 IS NULL;
(pointless...but symmetric with the others)
Hopefully this helps.
David J.
^ permalink raw reply [nested|flat] 12+ messages in thread
* RE: unique index with several columns
@ 2022-03-04 16:11 Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
parent: David G. Johnston <david.g.johnston@gmail.com>
0 siblings, 1 reply; 12+ messages in thread
From: Voillequin, Jean-Marc @ 2022-03-04 16:11 UTC (permalink / raw)
To: David G. Johnston <david.g.johnston@gmail.com>; +Cc: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Yes, it helps, thank you.
But I have many tables with many indexes and many columns!
Tons of combinations… ☹
From: David G. Johnston <david.g.johnston@gmail.com>
Sent: Friday, March 4, 2022 4:32 PM
To: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
Cc: pgsql-sql@lists.postgresql.org
Subject: Re: unique index with several columns
CAUTION: This email originated from outside of Moody's. Do not click links or open attachments unless you recognize the sender and know the content is safe.
On Fri, Mar 4, 2022 at 8:07 AM Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com<mailto:Jean-Marc.Voillequin@moodys.com>> wrote:
When one of the field is null, PG considers that the tuple is not the same:
('a',null) is not equal to ('a',null)
So, the unique constraint is not violated in PG.
But is there a way to have the same feature than Oracle?
I already tried with:
create unique index idx on t(coalesce(c1,''),coalesce(c2,''))
But in this case, I cannot insert several (null,null) without raising a duplicate key error.
You just said you wanted nulls to be considered equal to each other...
Not tested but these should work in conjunction with each other:
CREATE UNIQUE INDEX idx ON t (c1, c2) WHERE c1 IS NOT NULL AND c2 IS NOT NULL;
CREATE UNIQUE INDEX idx2 ON t (c1) WHERE c2 IS NULL AND c1 IS NOT NULL;
CREATE UNIQUE INDEX idx3 ON t (c2) WHERE c1 IS NULL AND c2 IS NOT NULL;
--CREATE INDEX idx4 ON t (c1, c2) WHERE c1 IS NULL AND c2 IS NULL; (pointless...but symmetric with the others)
Hopefully this helps.
David J.
-----------------------------------------
Moody's monitors email communications through its networks for regulatory compliance purposes and to protect its customers, employees and business and where allowed to do so by applicable law. The information contained in this e-mail message, and any attachment thereto, is confidential and may not be disclosed without our express permission. If you are not the intended recipient or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution or copying of this message, or any attachment thereto, in whole or in part, is strictly prohibited. If you have received this message in error, please immediately notify us by telephone, fax or e-mail and delete the message and all of its attachments. Every effort is made to keep our network free from viruses. You should, however, review this e-mail message, as well as any attachment thereto, for viruses. We take no responsibility and have no liability for any computer virus which may be transferred via this e-mail message.
-----------------------------------------
^ permalink raw reply [nested|flat] 12+ messages in thread
* Re: unique index with several columns
@ 2022-03-04 18:26 Alexey M Boltenkov <padrebolt@yandex.ru>
parent: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
0 siblings, 1 reply; 12+ messages in thread
From: Alexey M Boltenkov @ 2022-03-04 18:26 UTC (permalink / raw)
To: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; +Cc: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
You need the new v15 feature:
NULLS [NOT] DISTINCT
Specifies whether for a unique index, null values should be considered
distinct (not equal). The default is that they are distinct, so that a
unique index could contain multiple null values in a column.
https://www.postgresql.org/docs/devel/sql-createindex.html
On 03/04/22 19:11, Voillequin, Jean-Marc wrote:
>
> Yes, it helps, thank you.
>
> But I have many tables with many indexes and many columns!
>
> Tons of combinations… ☹
>
> *From:* David G. Johnston <david.g.johnston@gmail.com>
> *Sent:* Friday, March 4, 2022 4:32 PM
> *To:* Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
> *Cc:* pgsql-sql@lists.postgresql.org
> *Subject:* Re: unique index with several columns
>
> *CAUTION:*This email originated from outside of Moody's. Do not click
> links or open attachments unless you recognize the sender and know the
> content is safe.
>
> On Fri, Mar 4, 2022 at 8:07 AM Voillequin, Jean-Marc
> <Jean-Marc.Voillequin@moodys.com
> <mailto:Jean-Marc.Voillequin@moodys.com>> wrote:
>
> When one of the field is null, PG considers that the tuple is not
> the same:
>
> ('a',null) is not equal to ('a',null)
>
> So, the unique constraint is not violated in PG.
>
> But is there a way to have the same feature than Oracle?
>
> I already tried with:
>
> create unique index idx on t(coalesce(c1,''),coalesce(c2,''))
>
> But in this case, I cannot insert several (null,null) without
> raising a duplicate key error.
>
> You just said you wanted nulls to be considered equal to each other...
>
> Not tested but these should work in conjunction with each other:
>
> CREATE UNIQUE INDEX idx ON t (c1, c2) WHERE c1 IS NOT NULL AND c2 IS
> NOT NULL;
>
> CREATE UNIQUE INDEX idx2 ON t (c1) WHERE c2 IS NULL AND c1 IS NOT NULL;
>
> CREATE UNIQUE INDEX idx3 ON t (c2) WHERE c1 IS NULL AND c2 IS NOT NULL;
>
> --CREATE INDEX idx4 ON t (c1, c2) WHERE c1 IS NULL AND c2 IS NULL;
> (pointless...but symmetric with the others)
>
> Hopefully this helps.
>
> David J.
>
> -----------------------------------------
> Moody's monitors email communications through its networks for
> regulatory compliance purposes and to protect its customers, employees
> and business and where allowed to do so by applicable law. The
> information contained in this e-mail message, and any attachment
> thereto, is confidential and may not be disclosed without our express
> permission. If you are not the intended recipient or an employee or
> agent responsible for delivering this message to the intended
> recipient, you are hereby notified that you have received this message
> in error and that any review, dissemination, distribution or copying
> of this message, or any attachment thereto, in whole or in part, is
> strictly prohibited. If you have received this message in error,
> please immediately notify us by telephone, fax or e-mail and delete
> the message and all of its attachments. Every effort is made to keep
> our network free from viruses. You should, however, review this e-mail
> message, as well as any attachment thereto, for viruses. We take no
> responsibility and have no liability for any computer virus which may
> be transferred via this e-mail message.
> -----------------------------------------
^ permalink raw reply [nested|flat] 12+ messages in thread
* Re: unique index with several columns
@ 2022-03-04 18:32 Tom Lane <tgl@sss.pgh.pa.us>
parent: Alexey M Boltenkov <padrebolt@yandex.ru>
0 siblings, 2 replies; 12+ messages in thread
From: Tom Lane @ 2022-03-04 18:32 UTC (permalink / raw)
To: Alexey M Boltenkov <padrebolt@yandex.ru>; +Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Alexey M Boltenkov <padrebolt@yandex.ru> writes:
> You need the new v15 feature:
> NULLS [NOT] DISTINCT
That won't replicate the behavior shown by the OP though.
In particular, not the weird inconsistency for all-null rows.
regards, tom lane
^ permalink raw reply [nested|flat] 12+ messages in thread
* RE: unique index with several columns
@ 2022-03-04 18:57 Klaus Kaisersberger <woodconsult@outlook.de>
parent: Tom Lane <tgl@sss.pgh.pa.us>
1 sibling, 2 replies; 12+ messages in thread
From: Klaus Kaisersberger @ 2022-03-04 18:57 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; Alexey M Boltenkov <padrebolt@yandex.ru>; +Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
This should solve the task:
create unique index idx on t ((
case
when c1 is null and c2 is null then null
when c1 is null and c2 is not null then '{c2}'
when c1 is not null and c2 is null then '{c1}'
else '{c1,c2}'
end));
-----Original Message-----
From: Tom Lane <tgl@sss.pgh.pa.us>
Sent: Friday, March 4, 2022 7:32 PM
To: Alexey M Boltenkov <padrebolt@yandex.ru>
Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org
Subject: Re: unique index with several columns
Alexey M Boltenkov <padrebolt@yandex.ru> writes:
> You need the new v15 feature:
> NULLS [NOT] DISTINCT
That won't replicate the behavior shown by the OP though.
In particular, not the weird inconsistency for all-null rows.
regards, tom lane
^ permalink raw reply [nested|flat] 12+ messages in thread
* Re: unique index with several columns
@ 2022-03-04 19:06 David G. Johnston <david.g.johnston@gmail.com>
parent: Klaus Kaisersberger <woodconsult@outlook.de>
1 sibling, 0 replies; 12+ messages in thread
From: David G. Johnston @ 2022-03-04 19:06 UTC (permalink / raw)
To: Klaus Kaisersberger <woodconsult@outlook.de>; +Cc: Tom Lane <tgl@sss.pgh.pa.us>; Alexey M Boltenkov <padrebolt@yandex.ru>; Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
The convention on these lists is to inline or bottom post.
On Fri, Mar 4, 2022 at 11:57 AM Klaus Kaisersberger <woodconsult@outlook.de>
wrote:
> This should solve the task:
>
> create unique index idx on t ((
> case
> when c1 is null and c2 is null then null
> when c1 is null and c2 is not null then '{c2}'
> when c1 is not null and c2 is null then '{c1}'
> else '{c1,c2}'
> end));
>
>
I'm not sure what your '{c1}' syntax means but I'll take it you are
suggesting to construct an array. This seems to fail quite easily if the
values of c1 and c2 overlap.
David J.
^ permalink raw reply [nested|flat] 12+ messages in thread
* RE: unique index with several columns
@ 2022-03-04 19:18 Klaus Kaisersberger <klaus.kaisersberger@outlook.com>
parent: Klaus Kaisersberger <woodconsult@outlook.de>
1 sibling, 1 reply; 12+ messages in thread
From: Klaus Kaisersberger @ 2022-03-04 19:18 UTC (permalink / raw)
To: woodconsult@outlook.de <woodconsult@outlook.de>; Tom Lane <tgl@sss.pgh.pa.us>; Alexey M Boltenkov <padrebolt@yandex.ru>; +Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Sorry, mixed the lines up:
create unique index idx on t ((
case
when c1 is null and c2 is null then null
when c1 is null and c2 is not null then ARRAY[null,c2]
when c1 is not null and c2 is null then ARRAY[c1,null]
else ARRAY[c1,c2]
end
));
This could be generically extended to an arbitrary number of columns by counting the number of null column values in a separate function.
-----Original Message-----
From: Klaus Kaisersberger <woodconsult@outlook.de>
Sent: Friday, March 4, 2022 7:57 PM
To: Tom Lane <tgl@sss.pgh.pa.us>; Alexey M Boltenkov <padrebolt@yandex.ru>
Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org
Subject: RE: unique index with several columns
This should solve the task:
create unique index idx on t ((
case
when c1 is null and c2 is null then null
when c1 is null and c2 is not null then '{c2}'
when c1 is not null and c2 is null then '{c1}'
else '{c1,c2}'
end));
-----Original Message-----
From: Tom Lane <tgl@sss.pgh.pa.us>
Sent: Friday, March 4, 2022 7:32 PM
To: Alexey M Boltenkov <padrebolt@yandex.ru>
Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org
Subject: Re: unique index with several columns
Alexey M Boltenkov <padrebolt@yandex.ru> writes:
> You need the new v15 feature:
> NULLS [NOT] DISTINCT
That won't replicate the behavior shown by the OP though.
In particular, not the weird inconsistency for all-null rows.
regards, tom lane
^ permalink raw reply [nested|flat] 12+ messages in thread
* RE: unique index with several columns
@ 2022-03-04 20:02 Klaus Kaisersberger <woodconsult@outlook.de>
parent: Klaus Kaisersberger <klaus.kaisersberger@outlook.com>
0 siblings, 0 replies; 12+ messages in thread
From: Klaus Kaisersberger @ 2022-03-04 20:02 UTC (permalink / raw)
To: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Here a usable example for an arbitrary number of columns (might require casting the columns to e.g. bit varying before making the arrays):
Just replace c1,c2 with your (casted) number of columns on index creation.
create function fn(cs anyelement)
returns int
as
'select count(1) from unnest(cs) t(c) where c is not null;'
language sql
immutable;
create unique index idx on t ((
case
when fn(ARRAY[c1,c2])=0 then null
else ARRAY[c1,c2]
end
));
Result:
db=# insert into t(c1,c2) values (null,null);
INSERT 0 1
db=# insert into t(c1,c2) values (null,null);
INSERT 0 1
db=# insert into t(c1,c2) values (null,null);
INSERT 0 1
db=# insert into t(c1,c2) values (1,null);
INSERT 0 1
db=# insert into t(c1,c2) values (1,null);
ERROR: duplicate key value violates unique constraint "idx"
DETAIL: Key ((
CASE
WHEN fn(ARRAY[c1, c2]) = 0 THEN NULL::integer[]
ELSE ARRAY[c1, c2]
END))=({1,NULL}) already exists.
db=# insert into t(c1,c2) values (null,1);
INSERT 0 1
db=# insert into t(c1,c2) values (null,1);
ERROR: duplicate key value violates unique constraint "idx"
DETAIL: Key ((
CASE
WHEN fn(ARRAY[c1, c2]) = 0 THEN NULL::integer[]
ELSE ARRAY[c1, c2]
END))=({NULL,1}) already exists.
db=# insert into t(c1,c2) values (null,2);
INSERT 0 1
db=# insert into t(c1,c2) values (null,2);
ERROR: duplicate key value violates unique constraint "idx"
DETAIL: Key ((
CASE
WHEN fn(ARRAY[c1, c2]) = 0 THEN NULL::integer[]
ELSE ARRAY[c1, c2]
END))=({NULL,2}) already exists.
^ permalink raw reply [nested|flat] 12+ messages in thread
* Re: unique index with several columns
@ 2022-03-04 20:47 Alexey M Boltenkov <padrebolt@yandex.ru>
parent: Tom Lane <tgl@sss.pgh.pa.us>
1 sibling, 1 reply; 12+ messages in thread
From: Alexey M Boltenkov @ 2022-03-04 20:47 UTC (permalink / raw)
To: Tom Lane <tgl@sss.pgh.pa.us>; +Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
On 03/04/22 21:32, Tom Lane wrote:
> Alexey M Boltenkov <padrebolt@yandex.ru> writes:
>> You need the new v15 feature:
>> NULLS [NOT] DISTINCT
> That won't replicate the behavior shown by the OP though.
> In particular, not the weird inconsistency for all-null rows.
>
> regards, tom lane
>
But why?
# create table t(c1 char, c2 char);
CREATE TABLE
# create unique index idx on t(c1,c2) nulls not distinct where c1 is not
null or c2 is not null;
CREATE INDEX
# insert into t(c1,c2) values (null,null);
INSERT 0 1
# insert into t(c1,c2) values (null,null);
INSERT 0 1
# insert into t(c1,c2) values ('a',null);
INSERT 0 1
# insert into t(c1,c2) values ('a',null);
ERROR: 23505: duplicate key value violates unique constraint "idx"
DETAIL: Key (c1, c2)=(a, null) already exists.
SCHEMA NAME: public
TABLE NAME: t
CONSTRAINT NAME: idx
LOCATION: _bt_check_unique, nbtinsert.c:664
# \d+ t
Table "public.t"
Column │ Type │ Collation │ Nullable │ Default │ Storage │
Compression │ Stats target │ Description
════════╪══════════════╪═══════════╪══════════╪═════════╪══════════╪═════════════╪══════════════╪═════════════
c1 │ character(1) │ │ │ │ extended
│ │ │
c2 │ character(1) │ │ │ │ extended
│ │ │
Indexes:
"idx" UNIQUE, btree (c1, c2) NULLS NOT DISTINCT WHERE c1 IS NOT
NULL OR c2 IS NOT NULL
Access method: heap
# table t;
c1 │ c2
════╪════
¤ │ ¤
¤ │ ¤
a │ ¤
(3 rows)
^ permalink raw reply [nested|flat] 12+ messages in thread
* RE: unique index with several columns
@ 2022-03-08 16:59 Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
parent: Alexey M Boltenkov <padrebolt@yandex.ru>
0 siblings, 0 replies; 12+ messages in thread
From: Voillequin, Jean-Marc @ 2022-03-08 16:59 UTC (permalink / raw)
To: Alexey M Boltenkov <padrebolt@yandex.ru>; Tom Lane <tgl@sss.pgh.pa.us>; +Cc: David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Thanks a lot guys.
I'm waiting for the 15 release to implement Alexey solution.
But for now:
create unique index idx on t((array[c1,c2])) where not((c1,c2) is null);
will make the job
not((c1,c2) is null) is the tricky condition to check that not all fields are null...
Proof:
RRT=> create table t(c1 char,c2 char);
CREATE TABLE
RRT=> create unique index idx on t((array[c1,c2])) where not((c1,c2) is null);
CREATE INDEX
RRT=> insert into t values (null,null);
INSERT 0 1
RRT=> insert into t values (null,null);
INSERT 0 1
RRT=> insert into t values (null,'a');
INSERT 0 1
RRT=> insert into t values (null,'a');
ERROR: duplicate key value violates unique constraint "idx"
DETAIL: Key ((ARRAY[c1, c2]))=({NULL,a}) already exists.
Regards
-----Original Message-----
From: Alexey M Boltenkov <padrebolt@yandex.ru>
Sent: Friday, March 4, 2022 9:47 PM
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>; David G. Johnston <david.g.johnston@gmail.com>; pgsql-sql@lists.postgresql.org
Subject: Re: unique index with several columns
CAUTION: This email originated from outside of Moody's. Do not click links or open attachments unless you recognize the sender and know the content is safe.
On 03/04/22 21:32, Tom Lane wrote:
> Alexey M Boltenkov <padrebolt@yandex.ru> writes:
>> You need the new v15 feature:
>> NULLS [NOT] DISTINCT
> That won't replicate the behavior shown by the OP though.
> In particular, not the weird inconsistency for all-null rows.
>
> regards, tom lane
>
But why?
# create table t(c1 char, c2 char);
CREATE TABLE
# create unique index idx on t(c1,c2) nulls not distinct where c1 is not null or c2 is not null; CREATE INDEX # insert into t(c1,c2) values (null,null); INSERT 0 1 # insert into t(c1,c2) values (null,null); INSERT 0 1 # insert into t(c1,c2) values ('a',null); INSERT 0 1 # insert into t(c1,c2) values ('a',null);
ERROR: 23505: duplicate key value violates unique constraint "idx"
DETAIL: Key (c1, c2)=(a, null) already exists.
SCHEMA NAME: public
TABLE NAME: t
CONSTRAINT NAME: idx
LOCATION: _bt_check_unique, nbtinsert.c:664 # \d+ t
Table "public.t"
Column │ Type │ Collation │ Nullable │ Default │ Storage │ Compression │ Stats target │ Description ════════╪══════════════╪═══════════╪══════════╪═════════╪══════════╪═════════════╪══════════════╪═════════════
c1 │ character(1) │ │ │ │ extended │ │ │
c2 │ character(1) │ │ │ │ extended │ │ │
Indexes:
"idx" UNIQUE, btree (c1, c2) NULLS NOT DISTINCT WHERE c1 IS NOT NULL OR c2 IS NOT NULL Access method: heap # table t;
c1 │ c2
════╪════
¤ │ ¤
¤ │ ¤
a │ ¤
(3 rows)
-----------------------------------------
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^ permalink raw reply [nested|flat] 12+ messages in thread
end of thread, other threads:[~2022-03-08 16:59 UTC | newest]
Thread overview: 12+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2022-03-04 15:06 unique index with several columns Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
2022-03-04 15:09 ` Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
2022-03-04 15:32 ` David G. Johnston <david.g.johnston@gmail.com>
2022-03-04 16:11 ` Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
2022-03-04 18:26 ` Alexey M Boltenkov <padrebolt@yandex.ru>
2022-03-04 18:32 ` Tom Lane <tgl@sss.pgh.pa.us>
2022-03-04 18:57 ` Klaus Kaisersberger <woodconsult@outlook.de>
2022-03-04 19:06 ` David G. Johnston <david.g.johnston@gmail.com>
2022-03-04 19:18 ` Klaus Kaisersberger <klaus.kaisersberger@outlook.com>
2022-03-04 20:02 ` Klaus Kaisersberger <woodconsult@outlook.de>
2022-03-04 20:47 ` Alexey M Boltenkov <padrebolt@yandex.ru>
2022-03-08 16:59 ` Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
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