[NO ISSUE][DOC] Cleanup SQL compatibility list

- user model changes: no
- storage format changes: no
- interface changes: no

Details:
- Remove RIGHT OUTER JOIN and COALESCE function from the list
  of SQL incompatibilities because they have been implemented

Change-Id: I0f8df90b8eaf588b8e0d6bd620e650b7da72b94f
Reviewed-on: https://asterix-gerrit.ics.uci.edu/c/asterixdb/+/9764
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Dmitry Lychagin <dmitry.lychagin@couchbase.com>
Reviewed-by: Ali Alsuliman <ali.al.solaiman@gmail.com>
diff --git a/asterixdb/asterix-doc/src/main/markdown/sqlpp/6_sql_diff.md b/asterixdb/asterix-doc/src/main/markdown/sqlpp/6_sql_diff.md
index 7956f07..d5bc3cf 100644
--- a/asterixdb/asterix-doc/src/main/markdown/sqlpp/6_sql_diff.md
+++ b/asterixdb/asterix-doc/src/main/markdown/sqlpp/6_sql_diff.md
@@ -42,14 +42,12 @@
 The following SQL-92 features are not implemented yet. However, SQL++ does not conflict with these features:
 
   * CROSS JOIN, NATURAL JOIN, UNION JOIN
-  * RIGHT and FULL OUTER JOIN
+  * FULL OUTER JOIN
   * INTERSECT, EXCEPT, UNION with set semantics
   * CAST expression
-  * COALESCE expression
   * ALL and SOME predicates for linking to subqueries
   * UNIQUE predicate (tests a collection for duplicates)
   * MATCH predicate (tests for referential integrity)
   * Row and Table constructors
   * Preserved order for expressions in a SELECT list
 
-