fix: return null in getNString if the value is null

CHANGELOG.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## [0.8.4] - 2023-11-16
+## [0.8.4] - 2023-11-17
 
 ### Features
 - Support new SQL statements `SHOW CREATE TABLE`, `TRUNCATE` and [Alpha] `LEFT JOIN` (#3500 #3542 @dl239, #3576 @aceforeverd)
@@ -22,7 +22,7 @@
 - Tablet may crash after deleting an index in certain cases (#3561 @dl239)
 - There are some syntax errors in maintenance tools (#3545 @vagetablechicken)
 - Updating TTL fails if the deployment SQL contains multpile databases (#3503 @dl239)
-- Other minor bug fixes (#3518 #3567 @dl239, #3543 @aceforeverd, #3521 #3580 @vagetablechicken, #3594 #3597 @tobegit3hub)
+- Other minor bug fixes (#3518 #3567 #3604 @dl239, #3543 @aceforeverd, #3521 #3580 @vagetablechicken, #3594 #3597 @tobegit3hub)
 
 ### Code Refactoring
 #3547 @aceforeverd

java/openmldb-jdbc/src/main/java/com/_4paradigm/openmldb/jdbc/DirectResultSet.java

@@ -18,6 +18,7 @@
 
 import com._4paradigm.openmldb.common.codec.RowView;
 import com._4paradigm.openmldb.sdk.Schema;
+import com._4paradigm.openmldb.sdk.Common;
 
 import java.nio.ByteBuffer;
 import java.sql.*;
@@ -151,7 +152,10 @@ public Timestamp getTimestamp(int i) throws SQLException {
     public String getNString(int i) throws SQLException {
         int realIdx = i - 1;
         try {
-            return rowView.getString(realIdx);
+            if (rowView.isNull(realIdx)) {
+                return null;
+            }
+            return rowView.getValue(realIdx, Common.sqlType2ProtoType(schema.getColumnType(realIdx))).toString();
         } catch (Exception e) {
             throw new SQLException(e.getMessage());
         }

java/openmldb-jdbc/src/test/java/com/_4paradigm/openmldb/jdbc/RequestPreparedStatementTest.java

@@ -415,4 +415,80 @@ public void testDeploymentBatchRequest(String compressType, String storageMode)
             }
         }
     }
+
+    @Test
+    public void testResultSetNull() {
+        java.sql.Statement state = executor.getStatement();
+        String dbname = "db" + random.nextInt(100000);
+        String deploymentName = "dp_test1";
+        try {
+            state.execute("drop database if exists " + dbname + ";");
+            state.execute("create database " + dbname + ";");
+            state.execute("use " + dbname + ";");
+            String baseSql = "create table trans(c1 string,\n" +
+                    "                   c3 int,\n" +
+                    "                   c4 bigint,\n" +
+                    "                   c5 float,\n" +
+                    "                   c6 double,\n" +
+                    "                   c7 timestamp,\n" +
+                    "                   c8 date,\n" +
+                    "                   index(key=c1, ts=c7));";
+            state.execute(baseSql);
+            String selectSql = "SELECT c1, c3, sum(c4) OVER w1 as w1_c4_sum FROM trans WINDOW w1 AS " +
+                    "(PARTITION BY trans.c1 ORDER BY trans.c7 ROWS_RANGE BETWEEN 2s PRECEDING AND 0s OPEN PRECEDING EXCLUDE CURRENT_TIME);";
+            String deploySql = "DEPLOY " + deploymentName + " " + selectSql;
+            state.execute(deploySql);
+        } catch (SQLException e) {
+            e.printStackTrace();
+            Assert.fail();
+        }
+        PreparedStatement pstmt = null;
+        ResultSet resultSet = null;
+        try {
+            Thread.sleep(100);
+            pstmt = executor.getCallablePreparedStmt(dbname, deploymentName);
+
+            pstmt.setString(1, "aa");
+            pstmt.setInt(2, 20);
+            pstmt.setNull(3, Types.BIGINT);
+            pstmt.setFloat(4, 1.1f);
+            pstmt.setDouble(5, 2.1);
+            pstmt.setTimestamp(6, new Timestamp(0));
+            pstmt.setDate(7, Date.valueOf("2020-05-01"));
+
+            resultSet = pstmt.executeQuery();
+
+            Assert.assertEquals(resultSet.getMetaData().getColumnCount(), 3);
+            while (resultSet.next()) {
+                Assert.assertEquals(resultSet.getString(1), "aa");
+                Assert.assertEquals(resultSet.getNString(1), "aa");
+                Assert.assertEquals(resultSet.getInt(2), 20);
+                Assert.assertEquals(resultSet.getNString(2), "20");
+                Assert.assertTrue(resultSet.getNString(3) == null);
+            }
+
+            state.execute("drop deployment " + deploymentName + ";");
+            String drop = "drop table trans;";
+            boolean ok = executor.executeDDL(dbname, drop);
+            Assert.assertTrue(ok);
+            ok = executor.dropDB(dbname);
+            Assert.assertTrue(ok);
+        } catch (Exception e) {
+            e.printStackTrace();
+            Assert.fail();
+        } finally {
+            try {
+                state.close();
+                if (resultSet != null) {
+                    resultSet.close();
+                }
+                if (pstmt != null) {
+                    pstmt.close();
+                }
+            } catch (Exception throwables) {
+                throwables.printStackTrace();
+            }
+        }
+    }
+
 }