issue#1787: Non-standard MERGE throws LOCK_TIMEOUT_1

the match-index-to-key logic was wrong when there are more key columns than index columns

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

@@ -182,14 +182,17 @@ public class Merge extends CommandWithValues {
                     if (index != null) {
                         // verify the index columns match the key
                         Column[] indexColumns = index.getColumns();
-                        boolean indexMatchesKeys = true;
+                        boolean indexMatchesKeys;
                         if (indexColumns.length <= keys.length) {
+                            indexMatchesKeys = true;
                             for (int i = 0; i < indexColumns.length; i++) {
                                 if (indexColumns[i] != keys[i]) {
                                     indexMatchesKeys = false;
                                     break;
                                 }
                             }
+                        } else {
+                            indexMatchesKeys = false;
                         }
                         if (indexMatchesKeys) {
                             throw DbException.get(ErrorCode.CONCURRENT_UPDATE_1, targetTable.getName());

h2/src/test/org/h2/test/scripts/dml/merge.sql

@@ -46,13 +46,13 @@ EXPLAIN MERGE INTO TEST(ID, NAME) KEY(ID) VALUES(3, 'How do you do');
 >> MERGE INTO PUBLIC.TEST(ID, NAME) KEY(ID) VALUES (3, 'How do you do')
 
 MERGE INTO TEST(ID, NAME) KEY(NAME) VALUES(3, 'Fine');
-> exception LOCK_TIMEOUT_1
+> exception DUPLICATE_KEY_1
 
 MERGE INTO TEST(ID, NAME) KEY(NAME) VALUES(4, 'Fine!');
 > update count: 1
 
 MERGE INTO TEST(ID, NAME) KEY(NAME) VALUES(4, 'Fine! And you');
-> exception LOCK_TIMEOUT_1
+> exception DUPLICATE_KEY_1
 
 MERGE INTO TEST(ID, NAME) KEY(NAME, ID) VALUES(5, 'I''m ok');
 > update count: 1
@@ -94,3 +94,14 @@ SELECT * FROM TEST;
 
 DROP TABLE TEST;
 > ok
+
+-- Test for the index matching logic in org.h2.command.dml.Merge
+
+CREATE TABLE TEST(ID INT PRIMARY KEY, VALUE1 INT, VALUE2 INT, UNIQUE(VALUE1, VALUE2));
+> ok
+
+MERGE INTO TEST KEY (ID) VALUES (1, 2, 3), (2, 2, 3);
+> exception DUPLICATE_KEY_1
+
+DROP TABLE TEST;
+> ok