Sort mysql result by two column, but with a “holed” column - mysql

Question

I have the following initial situation:
+------------+-------------+
| legacyRank | forcedRank |
+------------+-------------+
| 0 | NULL |
| 1 | 6 |
| 2 | NULL |
| 3 | 1 |
| 4 | NULL |
| 5 | NULL |
| 6 | 2 |
+------------+-------------+
You could generate this table by the following schema:
CREATE TABLE two_column_order (
legacyRank VARCHAR(45),
forcedRank VARCHAR(45)
);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (5, NULL);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (6, 2);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (7, NULL);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (0, NULL);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (1, NULL);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (2, 6);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (3, NULL);
INSERT INTO two_column_order (legacyRank, forcedRank)
VALUES (4, 1);
SELECT * FROM two_column_order
order by
CASE when `forcedRank` <> NULL THEN `forcedRank`
ELSE `legacyRank`
END
The goal is to put each line with no-NULL forcedRank column in the accurate position mentioned in this forcedRank column. The expected rendering is like:
+------------+-------------+
| legacyRank | forcedRank |
+------------+-------------+
0 | 0 | NULL |
1 | 3 | 1 |
2 | 6 | 2 |
3 | 2 | NULL |
4 | 4 | NULL |
5 | 5 | NULL |
6 | 6 | 6 |
+------------+-------------+
As you see, each line take the position ordered by the forcedRank column if not NULL. When the the NULL rows still sorted by the legacyRank column in the positions leaved unoccupied by the non-NULL rows, but never shift the forced rows.
In this order, I tried to use the CASE WHEN syntax inside the ORDER BY like this:
SELECT * FROM two_column_order
order by
CASE WHEN (`forcedRank` is NULL ) THEN `legacyRank`
END ,
-`forcedRank` DESC,
`legacyRank`
But the result doesn’t really feat my expectations:
+------------+-------------+
| legacyRank | forcedRank |
+------------+-------------+
| 3 | 1 |
| 6 | 2 |
| 6 | 6 |
| 0 | NULL |
| 2 | NULL |
| 4 | NULL |
| 5 | NULL |
+------------+-------------+
So how can I make the legacyRank column get order beyond the forcedrank rows without shift them?

Answer 1

NULL can't tbe comapred like that you need to use ISor in your case IS NOT
SELECT * FROM two_column_order
order by
CASE when `forcedRank` IS NOT NULL THEN `forcedRank`
ELSE `legacyRank`
END
legacyRank
forcedRank
0
null
1
null
4
1
6
2
3
null
5
null
2
6
7
null
fiddle
As the first answer won't give you the correct answer.
i have changed the order by adding a decimal point to the original number so that it will be bigger than the new forced rank.
it will keep the order and a the forced number is smaller then the legayrank, it get you follwoing result
SELECT * FROM two_column_order
order by
CASE when `forcedRank` IS NOT NULL THEN `forcedRank`
ELSE `legacyRank` + .1
END
legacyRank
forcedRank
0
null
4
1
1
null
6
2
3
null
5
null
2
6
7
null
fiddle