Updating table of versioned rows with historical records in PostgreSQL

I have a master table of versioned rows:

CREATE TABLE master (
    id SERIAL PRIMARY KEY,
    rec_id integer, 
    val text, 
    valid_on date[], 
    valid_during daterange
);

INSERT INTO master (rec_id, val, valid_on, valid_during) VALUES
    (1, 'a', '{2015-01-01,2015-01-05}', '[2015-01-01,infinity)'),
    (2, 'b', '{2015-01-01,2015-01-05}', '[2015-01-01,infinity)'),
    (3, 'c', '{2015-01-01,2015-01-05}', '[2015-01-01,infinity)');

SELECT * FROM master ORDER BY rec_id, id;
/*
     id | rec_id | val |        valid_on         |     valid_during
    ----+--------+-----+-------------------------+-----------------------
      1 |      1 | a   | {2015-01-01,2015-01-05} | [2015-01-01,infinity)
      2 |      2 | b   | {2015-01-01,2015-01-05} | [2015-01-01,infinity)
      3 |      3 | c   | {2015-01-01,2015-01-05} | [2015-01-01,infinity)
*/

The rec_id is a the record's natural key, the valid_on is an array of dates on which the record was valid, and the valid_during is a date range describing the interval during which the record is valid. (The upper bound on the valid_during is 'infinity' if there is no record with the same rec_id with a more recent valid_on value.)

Given a second table of updated records, along with new dates on which each record was valid:

CREATE TABLE updates (id SERIAL PRIMARY KEY, rec_id integer, val text, valid_on date); 
INSERT INTO updates (rec_id, val, valid_on) VALUES
(1, 'a', '2015-01-03'), -- (1) same "val" for id 1, just add valid_on date
(2, 'd', '2015-01-06'), -- (2) different val for id 2,
(3, 'e', '2015-01-03'); -- (3) different val for id 3 with new date 
                        --     intersecting old date range

SELECT * FROM updates;
/*
     id | rec_id | val |  valid_on
    ----+--------+-----+------------
      1 |      1 | a   | 2015-01-03
      2 |      2 | d   | 2015-01-06
      3 |      3 | e   | 2015-01-03
*/

I would like to insert/update the master table to wind up with something like this:

1st case

You seem to forget the valid_during range. As your third case suggests, there can be multiple entries per (rec_id, val), so you must select the right one:

UPDATE master m
SET    valid_on = f_array_sort(m.valid_on || u.valid_on) -- sorted array, see below
FROM   updates u
WHERE  m.rec_id = u.rec_id 
AND    m.valid_during @> u.valid_on  -- additional check!
AND    m.val = u.val 
AND    NOT m.valid_on @> ARRAY[u.valid_on];

I assume the whole possible date range is always covered for each existing rec_id and valid_during shall not overlap per rec_id, or you'd have to do more.

After installing the additional module btree_gist, add an exclusion constraint to rule out overlapping date ranges if you don't have one, yet:

ALTER TABLE master ADD CONSTRAINT EXCLUDE
USING gist (rec_id WITH =, valid_during WITH &&)  -- disallow overlap

The GiST index this is implemented with is also a perfect match for the query. Details:

• Preventing adjacent/overlapping entries with EXCLUDE in PostgreSQL

• Store the day of the week and time?

2nd / 3rd case

Assuming that every date range starts with the smallest date in the (now sorted!) array: lower(m.valid_during) = m.valid_on[1]. I would enforce that with a CHECK constraint.

Here we need to create one or two new rows
In the 2nd case it is enough to shrink the range of the old row and insert one new row
In the 3rd case we update the old row with the left half of array and range, insert the new row and finally insert the with the right half of array and range.
Helper functions

To keep it simple I introduce a new constraint: every array is sorted. Use this helper function:

CREATE OR REPLACE FUNCTION f_array_sort(anyarray) 
  RETURNS anyarray LANGUAGE sql IMMUTABLE AS
$SELECT ARRAY(SELECT unnest($1) ORDER BY 1)$;

We don't need your helper function arraymin() any more, but it could be simplified to:

CREATE OR REPLACE FUNCTION f_array_min(anyarray) 
  RETURNS anyelement LANGUAGE sql IMMUTABLE AS
$SELECT min(a) FROM unnest($1) a$;

Two more to get the left and right half of an array split at a given element:

-- split left array at given element
CREATE OR REPLACE FUNCTION f_array_left(anyarray, anyelement) 
  RETURNS anyarray LANGUAGE sql IMMUTABLE AS
$SELECT ARRAY(SELECT * FROM unnest($1) a WHERE a = $2 ORDER BY 1)$;

Query

This does all the rest:

WITH u AS (  -- identify candidates
   SELECT m.id, rec_id, m.val, m.valid_on, m.valid_during
        , u.val AS u_val, u.valid_on AS u_valid_on
   FROM   master  m
   JOIN   updates u USING (rec_id)
   WHERE  m.val <> u.val
   AND    m.valid_during @> u.valid_on
   FOR    UPDATE  -- lock for update
   )
, upd1 AS (  -- case 2: no overlap, no split
   UPDATE master m  -- shrink old row
   SET    valid_during = daterange(lower(u.valid_during), u.u_valid_on)
   FROM   u
   WHERE  u.id = m.id
   AND    u.u_valid_on > m.valid_on[array_upper(m.valid_on, 1)]
   RETURNING m.id
   )
, ins1 AS (  -- insert new row
   INSERT INTO master (rec_id, val, valid_on, valid_during)
   SELECT u.rec_id, u.u_val, ARRAY[u.u_valid_on]
        , daterange(u.u_valid_on, upper(u.valid_during))
   FROM   upd1
   JOIN   u USING (id)
   )
, upd2 AS (  -- case 3: overlap, need to split row
   UPDATE master m  -- shrink to first half
   SET    valid_during = daterange(lower(u.valid_during), u.u_valid_on)
        , valid_on = f_array_left(u.valid_on, u.u_valid_on)
   FROM   u
   LEFT   JOIN upd1 USING (id)
   WHERE  upd1.id IS NULL  -- all others
   AND    u.id = m.id
   RETURNING m.id, f_array_right(u.valid_on, u.u_valid_on) AS arr_right
   )
INSERT INTO master (rec_id, val, valid_on, valid_during)
          -- new row
SELECT u.rec_id, u.u_val, ARRAY[u.u_valid_on]
     , daterange(u.u_valid_on, upd2.arr_right[1])
FROM   upd2
JOIN   u USING (id)
UNION ALL  -- second half of old row
SELECT u.rec_id, u.val, upd2.arr_right
     , daterange(upd2.arr_right[1], upper(u.valid_during))
FROM   upd2
JOIN   u USING (id);

db<>fiddle here

Old sqlfiddle
Notes

You need to understand the concept of data-modifying CTEs (writeable CTEs), before you touch this. Judging from the code you provided, you know your way around Postgres.

• Are SELECT type queries the only type that can be nested?

FOR UPDATE is to avoid race conditions with concurrent write access. If you are the only user writing to the tables, you don't need it.

I took a piece of paper and drew a timeline so not to get lost in all of this.

Each row is only updated / inserted once, and operations are simple and roughly optimized. No expensive window functions. This should perform well. Much faster than your previous approach in any case.

It would be a bit less confusing if you'd use distinct column names for u.valid_on and m.valid_on, which are related but different things.

I compute the right half of the split array in the RETURNING clause of CTE upd2: f_array_right(u.valid_on, u.u_valid_on) AS arr_right, because I nee

StackExchange Database Administrators Q#95845, answer score: 2