Detect missing WHEN in MERGE USING in Parser

h2/src/main/org/h2/command/Parser.java

@@ -1172,20 +1172,19 @@ public class Parser {
         command.setOnCondition(condition);
         read(")");
 
+        read("WHEN");
+        boolean matched = readIf("MATCHED");
+        if (matched) {
+            parseWhenMatched(command);
+        } else {
+            parseWhenNotMatched(command);
+        }
         if (readIf("WHEN")) {
-            boolean matched = readIf("MATCHED");
             if (matched) {
-                parseWhenMatched(command);
-            } else {
                 parseWhenNotMatched(command);
-            }
-            if (readIf("WHEN")) {
-                if (matched) {
-                    parseWhenNotMatched(command);
-                } else {
-                    read("MATCHED");
-                    parseWhenMatched(command);
-                }
+            } else {
+                read("MATCHED");
+                parseWhenMatched(command);
             }
         }
 

h2/src/main/org/h2/command/dml/MergeUsing.java

@@ -390,31 +390,21 @@ public class MergeUsing extends Prepared {
             query.prepare();
         }
 
-        int embeddedStatementsCount = 0;
-
         // Prepare each of the sub-commands ready to aid in the MERGE
         // collaboration
         if (updateCommand != null) {
             updateCommand.setSourceTableFilter(sourceTableFilter);
             updateCommand.setCondition(appendOnCondition(updateCommand));
             updateCommand.prepare();
-            embeddedStatementsCount++;
         }
         if (deleteCommand != null) {
             deleteCommand.setSourceTableFilter(sourceTableFilter);
             deleteCommand.setCondition(appendOnCondition(deleteCommand));
             deleteCommand.prepare();
-            embeddedStatementsCount++;
         }
         if (insertCommand != null) {
             insertCommand.setSourceTableFilter(sourceTableFilter);
             insertCommand.prepare();
-            embeddedStatementsCount++;
-        }
-
-        if (embeddedStatementsCount == 0) {
-            throw DbException.get(ErrorCode.SYNTAX_ERROR_1,
-                    "At least UPDATE, DELETE or INSERT embedded statement must be supplied.");
         }
 
         // setup the targetMatchQuery - for detecting if the target row exists

h2/src/test/org/h2/test/db/TestMergeUsing.java

@@ -161,7 +161,7 @@ public class TestMergeUsing extends TestBase implements Trigger {
                 GATHER_ORDERED_RESULTS_SQL,
                 "SELECT X AS ID, 'Marcy'||X AS NAME FROM SYSTEM_RANGE(1,3) WHERE X<0",
                 0,
-                "At least UPDATE, DELETE or INSERT embedded statement must be supplied.");
+                "expected \"WHEN\"");
         // Two updates to same row - update and delete together - emptying the
         // parent table
         testMergeUsing(