Merge branch 'grouping' of github.com:wricciot/links into grouping

CHANGES.md

@@ -1,6 +1,15 @@
 # Unreleased
 
 List of changes since the latest release.
+
+## Queries mixing set and bag semantics
+Links now provides experimental support for SQL queries with grouping and aggregation. These require the _mixing_ normaliser (`mixing_norm=on` in the configuration file).
+
+The result of grouping over a relation is represented as a finite map, which in Links is treated as a list of (grouping key, associated subrelation) pairs. Aggregation can then be applied groupwise to a finite map to obtain again a relation. Such Links queries are translated to SQL queries using `group by` and aggregates.
+
+Further information on this feature is provided in the [Links GitHub wiki](https://github.com/links-lang/links/wiki/Grouping-and-aggregation).
+
+## Other fixes/miscellaneous
 * The package `links-mysql`, based on the `mysql` opam package is no
   longer supported. Instead, the package `links-mysql8`, based on the
   `mysql8` package is provided, which also supports version of MySQL