Calculated field
REGEXP_EXTRACT_NTH([label], '(birch)-(birch)', 2)
Sample data
| label | quantity | amount | flag |
|---|---|---|---|
| cedar cedar | 65 | 12.8 | True |
| ORCHID-west | 66 | -7.6 | False |
| maple-east | 67 | 0 | null |
| willow north | 68 | 25.3 | True |
| birch-birch | 69 | 4.9 | False |
| pine/south | 70 | -1.2 | null |
| ash | 71 | 9 | True |
| null | null | null | null |
The same calculation as SQL
SELECT nullif(regexp_extract(label,'(birch)-(birch)',2),'') AS result FROM input
Runs the example above.
SELECT REGEXP_SUBSTR(label,'(birch)-(birch)',1,1,'e',2) AS result FROM input
Written for this dialect; not run here.
SELECT REGEXP_EXTRACT(label,r'birch-(birch)') AS result FROM input
Written for this dialect; not run here.
Result
| result |
|---|
| null |
| null |
| null |
| null |
| birch |
| null |
| null |
| null |
Same rows from the calculation and from the SQL in DuckDB.
Where a naive translation goes wrong
- Replacing REGEXP_EXTRACT_NTH with regexp_extract(label,'(birch)-(birch)',2) changes the shown values or null handling.
Naive SQL
SELECT regexp_extract(label,'(birch)-(birch)',2) AS result FROM input
result birch null Matches the calculation
SELECT nullif(regexp_extract(label,'(birch)-(birch)',2),'') AS result FROM input
result null null null null birch null null null
Signature
REGEXP_EXTRACT_NTH(string, constant_pattern, group)