On Sat, Mar 20, 2021 at 6:52 PM Ron Clarke <rclark...@gmail.com> wrote:
> /*
> I'm trying to port a system from SQL server, and at the same time better
> learn postgreSQL.
>
> I've come across a problem that is easily solved in that world, but I am
> struggling to find an approach in postgres that works.
>
> We have 2 sets of events A and B (sets), they have a shared number
> (ncode), both have unique Id's
>
> We want to link items of set A to those of set B, but each item of each
> set can only be linked once. That is we do not want to link all set 'A'
> items to all set 'B' Items with the same code.
>
> In SQL Server this is easy, we insert the records into a temporary table
> with separate Unique indexes on the id for set a and the ids for set b and
> put the 'ignore_dup_key' on which tells SQL Server to ignore duplicate rows
> and carry on.
>
> The nearest to this at first appears to be the ON CONFLICT ON CONSTRAINT
> IGNORE in Postgres. But this only works with a single constraint, at a time
> i.e. we can't set the ON CONFLICT ON CONSTRAINT IGNORE to work with
> multiple UNIQUE indexes.
>
> To show the problem:
>
> I'm using PostgreSQL version 11.
>
> */
> -- source data
> WITH sd AS (
> SELECT iid, s, ncode FROM (
> VALUES (1, 'A', 10),
> (2, 'A', 30),
> (3, 'A', 10),
> (4, 'B', 10),
> (5, 'B', 20),
> (6, 'B', 10)
> )
> AS tx (iid, s, ncode))
> SELECT iid, s, ncode FROM sd
>
> /* The target result would be :
>
> id:1, A, 10 this matches id:4, B, 10
> id:3, A, 10 this matches id:6, B, 10
> */
>
> -- Example to get the *wrong *answer, i.e. both sets of links
>
> WITH
> sd (i, s, n ) AS (
> SELECT iid, s, ncode FROM (
> VALUES (1, 'A', 10),
> (2, 'A', 30),
> (3, 'A', 10),
> (4, 'B', 10),
> (5, 'B', 20),
> (6, 'B', 10)
> )
> AS tx (iid, s, ncode))
> ,
> x AS ( SELECT
>
> ax.i as ia,
> ax.s as sa,
> ax.n as na,
> bx.i as ib,
> bx.s as sb,
> bx.n as nb,
> ROW_NUMBER () OVER (
>
> PARTITION BY bx.i
>
> ORDER BY
>
> ax.i ) as rx
>
> FROM sd AS ax
> INNER JOIN sd AS bx ON ax.n = bx.n and ax.i != bx.i and bx.s = 'B'
> WHERE ax.s = 'A'
> )
> SELECT ia,ib, na, rx FROM x
> ;
>
>
> /* I've tried using a recursive CTE where I'm trying to exclude results
> from the result set that have already been identified, but I can't get an
> allowed syntax.
> Doesn't seem to allow joins to the recursive term to exclude results.
> */
>
>
> /* I've tried Unique and Exclusion constraints on temporary table, e.g */
> -- similar Example to get the wrong answer, i.e. both sets of links
>
> DROP TABLE IF EXISTS links ;
>
> CREATE TEMPORARY TABLE links
> ( mid serial ,
> ia int ,
> -- ia int UNIQUE,
> ib int ,
> -- ib int UNIQUE,
> EXCLUDE USING gist (ia WITH =, ib WITH =)
>
> ) ;
>
> WITH
> sd (i, s, n ) AS (
> SELECT iid, side, ncode FROM (
> VALUES (1, 'A', 10),
> (2, 'A', 30),
> (3, 'A', 10),
> (4, 'B', 10),
> (5, 'B', 20),
> (6, 'B', 10)
> )
> AS tx (iid, side, ncode))
> ,
> x AS (
> SELECT
> ax.i as ia,
> ax.s as sa,
> ax.n as na,
> bx.i as ib,
> bx.s as sb,
> bx.n as nb,
> ROW_NUMBER () OVER (
> PARTITION BY bx.i
> ORDER BY
> ax.i
> ) as rx
> FROM sd AS ax
> INNER JOIN sd AS bx ON ax.n = bx.n and ax.i != bx.i and bx.s = 'B'
> WHERE ax.s = 'A'
> )
> -- SELECT * FROM x
> INSERT INTO links(ia,ib)
> SELECT ia, ib FROM x
> ON CONFLICT ON CONSTRAINT links_ia_ib_excl DO NOTHING;
>
> --
> SELECT * from links;
>
> /* I've also tried and failed to use array(ia,ib) within or as computed
> column of an Exclusion constraint of && s on temporary table, e.g
> but can't find any syntax that doesn't result in an error
> */
>
>
> DROP TABLE IF EXISTS links ;
>
> CREATE TEMPORARY TABLE links
> ( mid serial ,
> ia int ,
> -- ia int UNIQUE,
> ib int ,
> -- ib int UNIQUE,
> ix int[],
> EXCLUDE USING gist (ix WITH &&)
> ) ;
>
> -- This gives me:
> -- ERROR: data type integer[] has no default operator class for access
> method "gist"
>
> -- I have the btree_gist extension installed
>
>
> /*
>
> I appreciate I could create a cursor from a list of proposed links and
> step through each one, checking if the id value has been "used up"
> but I am trying to keep this as a set based operation to give me the
> results in one statement.
>
> There are some similar questions w.r.t. duplicate detection, but these
> again seem to be solved by evaluating each proposed record individually.
> If that's just what I have to do then so be it. There is probably a
> simple 'postgreSQL' freindly approach I'm still yet to discover having spent
> too long in Sybase and SQL Server worlds.
>
> Thanks for looking at this
>
> */
>
>
>
Hi Ron,
How about the code below.
It may require testing with more data.
WITH _sd AS (
SELECT iid, s, ncode FROM (
VALUES (1, 'A', 10),
(2, 'A', 30),
(3, 'A', 10),
(4, 'B', 10),
(5, 'B', 20),
(6, 'B', 10)
)
AS tx (iid, s, ncode)
)
--SELECT a.iid, a.s, a.ncode FROM _sd a;
,_sd__ab AS
(
SELECT
a.iid as iid__a, a.s AS s__a, a.ncode AS ncode__a
,b.iid as iid__b, b.s AS s__b, b.ncode AS ncode__b
FROM _sd a
JOIN _sd b ON b.ncode=a.ncode AND b.s>a.s
)
,_sd__ab__dist AS
(
SELECT
DISTINCT ON(
a.iid__a
,a.iid__b
)
a.iid__a, a.s__a, a.ncode__a
,a.iid__b, a.s__b, a.ncode__b
FROM _sd__ab a
ORDER BY
a.iid__a, a.iid__b, a.s__a, a.ncode__a
, a.s__b, a.ncode__b
)
,_sd__ab__dist2 AS
(
SELECT
a.iid__a, a.s__a, a.ncode__a
,a.iid__b, a.s__b, a.ncode__b
,a.iid__a__b__row_number1
,a.iid__a__b__row_number2
FROM
(
SELECT
a.iid__a, a.s__a, a.ncode__a
,a.iid__b, a.s__b, a.ncode__b
,ROW_NUMBER()OVER(PARTITION BY a.ncode__a,a.iid__a ORDER BY
a.iid__b)AS iid__a__b__row_number1
,ROW_NUMBER()OVER(PARTITION BY a.ncode__a,a.iid__b ORDER BY
a.iid__a)AS iid__a__b__row_number2
FROM _sd__ab__dist a
)a
)
SELECT a.*,ROW_NUMBER()OVER(ORDER BY a.iid__a)AS row_number FROM
_sd__ab__dist2 a WHERE a.iid__a__b__row_number1=iid__a__b__row_number2
;
Yields
iid__a | s__a | ncode__a | iid__b | s__b | ncode__b |
iid__a__b__row_number1 | iid__a__b__row_number2 | row_number
--------+------+----------+--------+------+----------+------------------------+------------------------+------------
1 | A | 10 | 4 | B | 10 |
1 | 1 | 1
3 | A | 10 | 6 | B | 10 |
2 | 2 | 2
(2 rows)
Time: 2.394 ms
-Allan.
>
>
>
