The MERGE statement now returns 0 as the generated key if the row was updated.

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

@@ -24,6 +24,7 @@ import org.h2.table.Column;
 import org.h2.table.Table;
 import org.h2.util.ObjectArray;
 import org.h2.value.Value;
+import org.h2.value.ValueLong;
 
 /**
  * This class represents the statement
@@ -106,6 +107,7 @@ public class Merge extends Prepared {
         String sql = buff.toString();
         update = session.prepare(sql);
         setCurrentRowNumber(0);
+        session.setLastIdentity(ValueLong.get(0));
         if (list.size() > 0) {
             count = 0;
             for (int x = 0; x < list.size(); x++) {

h2/src/main/org/h2/res/help.csv

@@ -82,8 +82,9 @@ MERGE INTO tableName [(columnName [,...])] [KEY(columnName [,...])]
 Updates the row if it exists, and if the row does not exist, inserts a new row.
 If the key columns are not specified, the primary key columns are used to find the row.
 This command is sometimes called 'UPSERT' as it updates a row if it exists,
-or inserts the row if it does not yet exist.
-If more than one row per new row is affected, an exception is thrown.
+or inserts the row if it does not yet exist. If more than one row per new row is affected,
+an exception is thrown. If the table contains an auto-incremented key or identity column, a
+nd the row was updated, the generated key is set to 0; otherwise it is set to the new key.
 ","
 MERGE INTO TEST KEY(ID) VALUES(2, 'World')
 "

h2/src/test/org/h2/test/jdbc/TestStatement.java

@@ -43,6 +43,7 @@ public class TestStatement extends TestBase {
         testConnectionRollback();
         testStatement();
         if (config.jdk14) {
+            testIdentityMerge();
             testIdentity();
         }
         conn.close();
@@ -318,6 +319,29 @@ public class TestStatement extends TestBase {
         stat.close();
     }
 
+    private void testIdentityMerge() throws SQLException {
+        Statement stat = conn.createStatement();
+        stat.execute("drop table if exists test1");
+        stat.execute("create table test1(id identity, x int)");
+        stat.execute("drop table if exists test2");
+        stat.execute("create table test2(id identity, x int)");
+        stat.execute("merge into test1(x) key(x) values(5)");
+        ResultSet keys;
+        keys = stat.getGeneratedKeys();
+        keys.next();
+        assertEquals(1, keys.getInt(1));
+        stat.execute("insert into test2(x) values(10), (11), (12)");
+        stat.execute("merge into test1(x) key(x) values(5)");
+        keys = stat.getGeneratedKeys();
+        keys.next();
+        assertEquals(0, keys.getInt(1));
+        stat.execute("merge into test1(x) key(x) values(6)");
+        keys = stat.getGeneratedKeys();
+        keys.next();
+        assertEquals(2, keys.getInt(1));
+        stat.execute("drop table test1, test2");
+    }
+
     private void testIdentity() throws SQLException {
         Statement stat = conn.createStatement();
         stat.execute("CREATE SEQUENCE SEQ");