Because QUANTILE uses equal-width histograms to partition the specified data, it does not partition the data equally using equal-height histograms. In other words, do not expect equal row counts per specified quantile. Expect empty quantile histograms when, for example, duplicate values for sort_expression are found in the data.
For example, consider the following simple SELECT statement.
SELECT itemNo, quantity, QUANTILE(10,quantity) FROM inventory;
The report might look like this.
| itemNo | quantity | Quantile(10, quantity) |
|---|---|---|
| 13 | 1 | 0 |
| 9 | 1 | 0 |
| 7 | 1 | 0 |
| 2 | 1 | 0 |
| 5 | 1 | 0 |
| 3 | 1 | 0 |
| 1 | 1 | 0 |
| 6 | 1 | 0 |
| 4 | 1 | 0 |
| 10 | 1 | 0 |
| 8 | 1 | 0 |
| 11 | 1 | 0 |
| 12 | 9 | 9 |
Because the quantile sort is on quantity, and there are only two quantity scores in the inventory table, there are no scores in the report for deciles 1 through 8.