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

LOG([amount], 2)

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 CASE WHEN amount>0 THEN ln(amount)/ln(2) ELSE NULL END AS result FROM input ORDER BY id

Runs the example above.

SELECT CASE WHEN amount>0 THEN ln(amount)/ln(2) ELSE NULL END AS result FROM input ORDER BY id

Written for this dialect; not run here.

SELECT CASE WHEN amount>0 THEN ln(amount)/ln(2) ELSE NULL END 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	null
2	0	0	0	null
3	1.5	3	0.25	0.584963
4	4	4	0.5	2
5	9	5	0.8	3.16993
6	16	6	1	4
7	null	7	null	null
8	4	8	-0.5	2

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

Where a naive translation goes wrong

The default base-ten logarithm differs from the requested base two.
Naive SQL
```
SELECT CASE WHEN amount>0 THEN log10(amount) ELSE NULL END AS result FROM input ORDER BY id
```
id amount units score result
1 -2.5 2 -0.8 null
2 0 0 0 null
3 1.5 3 0.25 0.176091
4 4 4 0.5 0.60206
5 9 5 0.8 0.954243
6 16 6 1 1.20412
7 null 7 null null
8 4 8 -0.5 0.60206
Matches the calculation
```
SELECT CASE WHEN amount>0 THEN ln(amount)/ln(2) ELSE NULL END AS result FROM input ORDER BY id
```
id amount units score result
1 -2.5 2 -0.8 null
2 0 0 0 null
3 1.5 3 0.25 0.584963
4 4 4 0.5 2
5 9 5 0.8 3.16993
6 16 6 1 4
7 null 7 null null
8 4 8 -0.5 2

LOG(number, [number])