How to build an intercalated ranking from two tables using BigQuery - sql

Question

I have two tables in BigQuery with records ordered by a ranking. Given a ratio of integers, I want to be able to join both tables, keeping the order of the ranking and the proportions of the ratio of integers.
For example:
Table A
Name
Ranking A
Kevin
1
Jack
2
Kate
3
Randall
4
Beck
5
Table B:
Name
Ranking B
William
1
Laurel
2
Sophie
3
Tess
4
Deja
5
Toby
6
Nick
7
Given a ratio 2:3 where 2 corresponds with Table A, and 3 corresponds with Table B, the expected result would be:
Name
Ranking A
Ranking B
Final Rank
Kevin
1
1
Jack
2
2
William
1
3
Laurel
2
4
Sophie
3
5
Kate
3
6
Randall
4
7
Tess
4
8
Deja
5
9
Toby
6
10
Beck
5
11
Nick
7
12
Any ideas?

Answer 1

You can solve this problem with some math trick here. In both tables you have to compute a running sum and skip 2 (for second table) or 3 (for first table) values according to the ranking value you're currently placing. Basically you're making two gapped running sum, where the gaps will be filled by the other one's ranking values.
SELECT Name,
SUM(CASE WHEN MOD(RankingA,2) = 1 THEN 4 ELSE 1 END) OVER(ORDER BY RankingA)-3 AS rn
FROM tableA
UNION ALL
SELECT Name,
SUM(CASE WHEN MOD(RankingB,3) = 1 THEN 3 ELSE 1 END) OVER(ORDER BY RankingB) AS rn
FROM tableB
ORDER BY rn
Then you just apply the UNION ALL operation and ORDER BY on the just generated ranking.

Answer 2

Another approach would be:
SELECT name,
IF(tbl = 1, rank, NULL) AS rankingA,
IF(tbl = 2, rank, NULL) AS rankingB,
ROW_NUMBER() OVER (ORDER BY rank_grp, tbl, rank) final_rank
FROM (
SELECT name, rankingA AS rank, DIV(rankingA - 1, 2) AS rank_grp, 1 AS tbl FROM tableA
UNION ALL
SELECT name, rankingB, DIV(rankingB - 1, 3), 2 FROM tableB
);
+---------+----------+----------+------------+
| name | rankingA | rankingB | final_rank |
+---------+----------+----------+------------+
| Kevin | 1 | | 1 |
| Jack | 2 | | 2 |
| William | | 1 | 3 |
| Laurel | | 2 | 4 |
| Sophie | | 3 | 5 |
| Kate | 3 | | 6 |
| Randall | 4 | | 7 |
| Tess | | 4 | 8 |
| Deja | | 5 | 9 |
| Toby | | 6 | 10 |
| Beck | 5 | | 11 |
| Nick | | 7 | 12 |
+---------+----------+----------+------------+

Answer 3

You may try the following:
select Name, RankingA, RankingB,
rank() over (order by NewRank) FinalRank
from
(
select Name, cast(RankingA as string) as RankingA , '' as RankingB,
RankingA + floor((RankingA-1)/2)*3 as NewRank
from TableA
union all
select Name, '', cast(RankingB as string),
RankingB + ceiling((RankingB)/3)*2
from TableB
) T
RankingA + floor((RankingA-1)/2)*3: shifts each two consecutive RankingA values (1,2 and 3,4 and 5,6 ...) by n * 3 where n starts from 0.
RankingB + ceiling((RankingB)/3)*2: shifts each three consecutive RankingB values (1,2,3 and 4,5,6 ...) by n * 2 where n starts from 1.