Function Reference
The plugin provides 65 SQL functions organized into 8 sketch families. Each family has:
- Aggregation functions that build sketches from raw data (
ds_*_sketch) or merge existing sketches (ds_*_union) - Scalar functions that query sketches (estimate, quantile, merge, stringify, etc.)
All sketches are represented as VARBINARY in SQL.
Quick Lookup
| I want to… | Function |
|---|---|
| Count distinct values | ds_hll_sketch + ds_hll_estimate |
| Count distinct with set operations | ds_theta_sketch + ds_theta_estimate / ds_theta_intersection / ds_theta_exclude |
| Compute percentiles | ds_kll_sketch + ds_kll_quantile |
| Find the rank of a value | ds_kll_sketch + ds_kll_rank |
| Find frequent items | ds_freq_sketch + ds_freq_frequent_items |
| Compare two distributions (A/B test) | ds_tuple_doubles_sketch + ds_tuple_doubles_ttest |
| Compute Jaccard similarity | ds_theta_sketch + ds_theta_similarity |
| Merge pre-aggregated sketches | ds_*_union (aggregation) or ds_*_merge (scalar, pairwise) |
Conventions
- NULL sketch arguments to scalar functions return
NULL - NULL input values in aggregation functions are silently skipped
- All sketches support a
ds_*_stringifyfunction that returns a human-readable summary - Accuracy parameters (
lgK,k,nominalEntries) trade memory for precision — higher values = more accurate but larger sketches