6.2Processing
Processing options enable transforming results of a query according to the programmer’s needs, such as ordering or truncating. These options are optional and may be used to create a (linear) pipeline for further processing result sets returned by DATA QUERY LANGUAGE (DQL) and DATA INTROSPECTION LANGUAGE (DIL) operations. In case a pipeline is composed of two or more options, the order in which they are used affects the final outcome (e.g. using ORDER ASC followed by TOP 2 in a result set composed of 4, 2, 3, and 1 returns 1 and 2; using these same two options in reverse order – i.e. TOP 2 followed by ORDER ASC – returns 2 and 4 instead). The next subsections describe the processing options provided by HDFql.
| Processing Option | Description |
|---|---|
| ORDER | Order (i.e. sort) a result set in an ascending, descending, or reverse way |
| TOP | Truncate a result set after a certain given position from the top |
| BOTTOM | Truncate a result set after a certain given position from the bottom |
| FROM TO | Retain a result set within a certain given range |
| STEP | Step (i.e. jump) through a result set at every given position |
Table 6.4 – HDFql processing options