Document UNION evaluation order.

h2/src/docsrc/help/help.csv

@@ -21,6 +21,10 @@ LIMIT limits the number of rows returned by the query, OFFSET specified
 how many rows to skip. SAMPLE_SIZE limits the number of rows read for
 aggregate queries.
 
+Multiple set operators (UNION/INTERSECT/MINUS/EXPECT) are evaluated
+from left to right. For compatibility with other databases and future versions
+of H2 please use parentheses.
+
 If FOR UPDATE is specified, the tables are locked for writing.
 ","
 SELECT * FROM TEST;

h2/src/docsrc/html/roadmap.html

@@ -473,6 +473,7 @@ See also <a href="build.html#providing_patches">Providing Patches</a>.
 </li><li>Automatic mixed mode: support a port range list (to avoid firewall problems).
 </li><li>Support the pseudo column rowid, oid, _rowid_.
 </li><li>Support TRUNCATE for linked tables.
+</li><li>UNION: evaluate INTERSECT before UNION (like most other database except Oracle).
 </li></ul>
 
 <h2>Not Planned</h2>

h2/src/tools/org/h2/build/doc/dictionary.txt

@@ -629,4 +629,4 @@ sweden abbreviated xmx trede googlecode gustav standing hashes
 decompressed expansion ziv abbreviated augments omitted gain
 subtracted maxed logical lempel increases sibling impersonate proper remembers
 moon centric adeptia workflows generalized bpchar binaries incremental poor
-slowly prefs
+slowly prefs precedence