GREATEST in Tableau: the SQL equivalent, with a worked example

GREATEST([amount], [other])

id	amount	units	score	other
1	-2.5	2	-0.8	3
2	0	0	0	4
3	1.5	3	0.25	2
4	4	4	0.5	8
5	9	5	0.8	11
6	16	6	1	14
7	null	7	null	9
8	4	8	-0.5	null

SELECT greatest(amount,other) AS result FROM input ORDER BY id

Runs the example above.

SELECT GREATEST_IGNORE_NULLS(amount,other) AS result FROM input ORDER BY id

Written for this dialect; not run here.

SELECT (SELECT max(v) FROM unnest([amount,other]) AS v) AS result FROM input ORDER BY id

Written for this dialect; not run here.

id	amount	units	score	result
1	-2.5	2	-0.8	3
2	0	0	0	4
3	1.5	3	0.25	2
4	4	4	0.5	8
5	9	5	0.8	11
6	16	6	1	16
7	null	7	null	9
8	4	8	-0.5	4

Same rows from the calculation and from the SQL in DuckDB.

Where a naive translation goes wrong

Null-propagating extrema discard a present argument.
Naive SQL
```
SELECT CASE WHEN amount IS NULL OR other IS NULL THEN NULL ELSE greatest(amount,other) END AS result FROM input ORDER BY id
```
id amount units score result
1 -2.5 2 -0.8 3
2 0 0 0 4
3 1.5 3 0.25 2
4 4 4 0.5 8
5 9 5 0.8 11
6 16 6 1 16
7 null 7 null null
8 4 8 -0.5 null
Matches the calculation
```
SELECT greatest(amount,other) AS result FROM input ORDER BY id
```
id amount units score result
1 -2.5 2 -0.8 3
2 0 0 0 4
3 1.5 3 0.25 2
4 4 4 0.5 8
5 9 5 0.8 11
6 16 6 1 16
7 null 7 null 9
8 4 8 -0.5 4

GREATEST(number, number, ...)