Find "n" consecutive free numbers from table

Question

I have some table with numbers like this (status is either FREE or ASSIGNED)

id_set  number  status         
-----------------------
1       000001  ASSIGNED
1       000002  FREE
1       000003  ASSIGNED
1       000004  FREE
1       000005  FREE
1       000006  ASSIGNED
1       000007  ASSIGNED
1       000008  FREE
1       000009  FREE
1       000010  FREE
1       000011  ASSIGNED
1       000012  ASSIGNED
1       000013  ASSIGNED
1       000014  FREE
1       000015  ASSIGNED

and I need to find "n" consecutive numbers, so for n = 3, query would return

1       000008  FREE
1       000009  FREE
1       000010  FREE

It should return only first possible group of each id_set (in fact, it would be executed only for id_set per query)

I was checking WINDOW functions, tried some queries like COUNT(id_number) OVER (PARTITION BY id_set ROWS UNBOUNDED PRECEDING), but that's all I got :) I couldn't think of logic, how to do that in Postgres.

I was thinking about creating virtual column using WINDOW functions counting preceding rows for every number where status = 'FREE', then select first number, where count is equal to my "n" number.

Or maybe group numbers by status, but only from one ASSIGNED to another ASSIGNED and select only groups containing at least "n" numbers

EDIT

I found this query (and changed it a little bit)

WITH q AS
(
  SELECT *,
         ROW_NUMBER() OVER (PARTITION BY id_set, status ORDER BY number) AS rnd,
         ROW_NUMBER() OVER (PARTITION BY id_set ORDER BY number) AS rn
  FROM numbers
)
SELECT id_set,
       MIN(number) AS first_number,
       MAX(number) AS last_number,
       status,
       COUNT(number) AS numbers_count
FROM q
GROUP BY id_set,
         rnd - rn,
         status
ORDER BY
     first_number

which produces groups of FREE/ASSIGNED numbers, but I would like to have all numbers from only first group which meets the condition

SQL Fiddle

Answer 1

This is a gaps-and-islands problem. Assuming there are no gaps or duplicates in the same id_set set:

WITH partitioned AS (
  SELECT
    *,
    number - ROW_NUMBER() OVER (PARTITION BY id_set) AS grp
  FROM atable
  WHERE status = 'FREE'
),
counted AS (
  SELECT
    *,
    COUNT(*) OVER (PARTITION BY id_set, grp) AS cnt
  FROM partitioned
)
SELECT
  id_set,
  number
FROM counted
WHERE cnt >= 3
;

Here's a SQL Fiddle demo^* link for this query: http://sqlfiddle.com/#!1/a2633/1.

UPDATE

To return only one set, you could add in one more round of ranking:

WITH partitioned AS (
  SELECT
    *,
    number - ROW_NUMBER() OVER (PARTITION BY id_set) AS grp
  FROM atable
  WHERE status = 'FREE'
),
counted AS (
  SELECT
    *,
    COUNT(*) OVER (PARTITION BY id_set, grp) AS cnt
  FROM partitioned
),
ranked AS (
  SELECT
    *,
    RANK() OVER (ORDER BY id_set, grp) AS rnk
  FROM counted
  WHERE cnt >= 3
)
SELECT
  id_set,
  number
FROM ranked
WHERE rnk = 1
;

Here's a demo for this one too: http://sqlfiddle.com/#!1/a2633/2.

If you ever need to make it one set per id_set, change the RANK() call like this:

RANK() OVER (PARTITION BY id_set ORDER BY grp) AS rnk

Additionally, you could make the query return the smallest matching set (i.e. first try to return the first set of exactly three consecutive numbers if it exists, otherwise four, five etc.), like this:

RANK() OVER (ORDER BY cnt, id_set, grp) AS rnk

or like this (one per id_set):

RANK() OVER (PARTITION BY id_set ORDER BY cnt, grp) AS rnk

---

_{* The SQL Fiddle demos linked in this answer use the 9.1.8 instance as the 9.2.1 one doesn't appear to be working at the moment.}

Answer 2

A simple and fast variant:

SELECT min(number) AS first_number, count(*) AS ct_free
FROM (
    SELECT *, number - row_number() OVER (PARTITION BY id_set ORDER BY number) AS grp
    FROM   tbl
    WHERE  status = 'FREE'
    ) x
GROUP  BY grp
HAVING count(*) >= 3  -- minimum length of sequence only goes here
ORDER  BY grp
LIMIT  1;

• Requires a gapless sequence of numbers in number (as provided in the question).

• Works for any number of possible values in status besides 'FREE', even with NULL.

• The major feature is to subtract row_number() from number after eliminating non-qualifying rows. Consecutive numbers end up in the same grp - and grp is also guaranteed to be in ascending order.

• Then you can GROUP BY grp and count the members. Since you seem to want the first occurrence, ORDER BY grp LIMIT 1 and you get starting position and length of the sequence (can be >= n).

Set of rows

To get an actual set of numbers, don't look up the table another time. Much cheaper with generate_series():

SELECT generate_series(first_number, first_number + ct_free - 1)
    -- generate_series(first_number, first_number + 3 - 1) -- only 3
FROM  (
   SELECT min(number) AS first_number, count(*) AS ct_free
   FROM  (
      SELECT *, number - row_number() OVER (PARTITION BY id_set ORDER BY number) AS grp
      FROM   tbl
      WHERE  status = 'FREE'
      ) x
   GROUP  BY grp
   HAVING count(*) >= 3
   ORDER  BY grp
   LIMIT  1
   ) y;

If you actually want a string with leading zeros like you display in your example values, use to_char() with the FM (fill mode) modifier:

SELECT to_char(generate_series(8, 11), 'FM000000')

SQL Fiddle with extended test case and both queries.

Closely related answer:

• Select longest continuous sequence

Answer 3

This is a fairly generic way to do this.

Bear in mind it depends on your number column being consecutive. If it's not a Window function and/or CTE type-solution will probably be needed:

SELECT 
    number
FROM
    mytable m
CROSS JOIN
   (SELECT 3 AS consec) x
WHERE 
    EXISTS
       (SELECT 1 
        FROM mytable
        WHERE number = m.number - x.consec + 1
        AND status = 'FREE')
    AND NOT EXISTS
       (SELECT 1 
        FROM mytable
        WHERE number BETWEEN m.number - x.consec + 1 AND m.number
        AND status = 'ASSIGNED')

Answer 4

This will return only the first of the 3 numbers. It does not require that the values of number are consecutive. Tested at SQL-Fiddle:

WITH cte3 AS
( SELECT
    *,
    COUNT(CASE WHEN status = 'FREE' THEN 1 END) 
        OVER (PARTITION BY id_set ORDER BY number
              ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING)
      AS cnt
  FROM atable
)
SELECT
  id_set, number
FROM cte3
WHERE cnt = 3 ;

And this will show all numbers (where there are 3 or more consecutive 'FREE' positions):

WITH cte3 AS
( SELECT
    *,
    COUNT(CASE WHEN status = 'FREE' THEN 1 END) 
        OVER (PARTITION BY id_set ORDER BY number
              ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING)
      AS cnt
  FROM atable
)
, cte4 AS
( SELECT
    *, 
    MAX(cnt) 
        OVER (PARTITION BY id_set ORDER BY number
              ROWS BETWEEN 2 PRECEDING AND CURRENT ROW)
      AS maxcnt
  FROM cte3
)
SELECT
  id_set, number
FROM cte4
WHERE maxcnt >= 3 ;

Answer 5

select r1.number from some_table r1, 
some_table r2,
some_table r3,
some_table r4 
where r3.number <= r2.number 
and r3.number >= r1.number 
and r3.status = 'FREE' 
and r2.number = r1.number + 4 
and r4.number <= r2.number 
and r4.number >= r1.number 
and r4.status = 'ASSIGNED'
group by r1.number, r2.number having count(r3.number) = 5 and count(r4.number) = 0 order by r1.number asc limit 1 ;

In this case 5 consecutive numbers - therefore difference must be 4 or in other words count(r3.number) = n and r2.number = r1.number + n - 1.

With joins:

select r1.number 
from some_table r1 join 
 some_table r2 on (r2.number = r1.number + :n -1) join
 some_table r3 on (r3.number <= r2.number and r3.number >= r1.number) join
 some_table r4 on (r4.number <= r2.number and r4.number >= r1.number)
where  
 r3.status = 'FREE' and
 r4.status = 'ASSIGNED'
group by r1.number, r2.number having count(r3.number) = :n and count(r4.number) = 0 order by r1.number asc limit 1 ;

Answer 6

CREATE TABLE #ConsecFreeNums
(
     id_set BIGINT
    ,number VARCHAR(10)
    ,status VARCHAR(10)
)

CREATE TABLE #ConsecFreeNumsResult
(
     Seq    INT
    ,id_set BIGINT
    ,number VARCHAR(10)
    ,status VARCHAR(10)
)

INSERT #ConsecFreeNums
SELECT 1, '000002', 'FREE' UNION
SELECT 1, '000003', 'ASSIGNED' UNION
SELECT 1, '000004', 'FREE' UNION
SELECT 1, '000005', 'FREE' UNION
SELECT 1, '000006', 'ASSIGNED' UNION
SELECT 1, '000007', 'ASSIGNED' UNION
SELECT 1, '000008', 'FREE' UNION
SELECT 1, '000009', 'FREE' UNION
SELECT 1, '000010', 'FREE' UNION
SELECT 1, '000011', 'ASSIGNED' UNION
SELECT 1, '000012', 'ASSIGNED' UNION
SELECT 1, '000013', 'ASSIGNED' UNION
SELECT 1, '000014', 'FREE' UNION
SELECT 1, '000015', 'ASSIGNED'

DECLARE @id_set AS BIGINT, @number VARCHAR(10), @status VARCHAR(10), @number_count INT, @number_count_check INT

DECLARE ConsecFreeNumsCursor CURSOR FAST_FORWARD FOR
SELECT
       id_set
      ,number
      ,status
 FROM
      #ConsecFreeNums
WHERE id_set = 1
ORDER BY number

OPEN ConsecFreeNumsCursor

FETCH NEXT FROM ConsecFreeNumsCursor INTO @id_set, @number, @status

SET @number_count_check = 3
SET @number_count = 0

WHILE @@FETCH_STATUS = 0
BEGIN
    IF @status = 'ASSIGNED'
    BEGIN
        IF @number_count = @number_count_check
        BEGIN
            SELECT 'Results'
            SELECT * FROM #ConsecFreeNumsResult ORDER BY number
            BREAK
        END
        SET @number_count = 0
        TRUNCATE TABLE #ConsecFreeNumsResult
    END
    ELSE
    BEGIN
        SET @number_count = @number_count + 1
        INSERT #ConsecFreeNumsResult SELECT @number_count, @id_set, @number, @status
    END
    FETCH NEXT FROM ConsecFreeNumsCursor INTO @id_set, @number, @status
END

CLOSE ConsecFreeNumsCursor
DEALLOCATE ConsecFreeNumsCursor

DROP TABLE #ConsecFreeNums
DROP TABLE #ConsecFreeNumsResult