[fix](statistics)Fix sample min max npe bug.

fe/fe-core/src/main/java/org/apache/doris/statistics/OlapAnalysisTask.java

@@ -31,10 +31,8 @@
 import com.google.common.annotations.VisibleForTesting;
 import org.apache.commons.text.StringSubstitutor;
 
-import java.nio.charset.StandardCharsets;
 import java.security.SecureRandom;
 import java.util.ArrayList;
-import java.util.Base64;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -94,8 +92,8 @@ protected void doSample() throws Exception {
             // Get basic stats, including min and max.
             ResultRow basicStats = collectBasicStat(r);
             long rowCount = tbl.getRowCount();
-            String min = Base64.getEncoder().encodeToString(basicStats.get(0).getBytes(StandardCharsets.UTF_8));
-            String max = Base64.getEncoder().encodeToString(basicStats.get(1).getBytes(StandardCharsets.UTF_8));
+            String min = StatisticsUtil.encodeValue(basicStats, 0);
+            String max = StatisticsUtil.encodeValue(basicStats, 1);
 
             boolean limitFlag = false;
             long rowsToSample = pair.second;

fe/fe-core/src/main/java/org/apache/doris/statistics/StatisticsRepository.java

@@ -35,8 +35,6 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
-import java.nio.charset.StandardCharsets;
-import java.util.Base64;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -271,10 +269,8 @@ public static void alterColumnStatistics(AlterColumnStatsStmt alterColumnStatsSt
         params.put("count", String.valueOf(columnStatistic.count));
         params.put("ndv", String.valueOf(columnStatistic.ndv));
         params.put("nullCount", String.valueOf(columnStatistic.numNulls));
-        params.put("min", min == null ? "NULL" :
-                Base64.getEncoder().encodeToString(min.getBytes(StandardCharsets.UTF_8)));
-        params.put("max", max == null ? "NULL" :
-                Base64.getEncoder().encodeToString(max.getBytes(StandardCharsets.UTF_8)));
+        params.put("min", StatisticsUtil.encodeString(min));
+        params.put("max", StatisticsUtil.encodeString(max));
         params.put("dataSize", String.valueOf(columnStatistic.dataSize));
 
         if (partitionIds.isEmpty()) {

fe/fe-core/src/main/java/org/apache/doris/statistics/util/StatisticsUtil.java

@@ -90,12 +90,14 @@
 import org.apache.logging.log4j.Logger;
 
 import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
 import java.text.SimpleDateFormat;
 import java.time.LocalTime;
 import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Base64;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
@@ -936,4 +938,19 @@ public static int getAnalyzeTimeout() {
         return StatisticConstants.ANALYZE_TIMEOUT_IN_SEC;
     }
 
+    public static String encodeValue(ResultRow row, int index) {
+        if (row == null || row.getValues().size() <= index) {
+            return "NULL";
+        }
+        return encodeString(row.get(index));
+    }
+
+    public static String encodeString(String value) {
+        if (value == null) {
+            return "NULL";
+        } else {
+            return Base64.getEncoder().encodeToString(value.getBytes(StandardCharsets.UTF_8));
+        }
+    }
+
 }

fe/fe-core/src/test/java/org/apache/doris/statistics/util/StatisticsUtilTest.java

@@ -20,14 +20,19 @@
 import org.apache.doris.catalog.Type;
 import org.apache.doris.common.AnalysisException;
 import org.apache.doris.qe.SessionVariable;
+import org.apache.doris.statistics.ResultRow;
 
+import com.google.common.collect.Lists;
 import mockit.Mock;
 import mockit.MockUp;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import java.nio.charset.StandardCharsets;
 import java.time.LocalTime;
 import java.time.format.DateTimeFormatter;
+import java.util.ArrayList;
+import java.util.Base64;
 
 public class StatisticsUtilTest {
     @Test
@@ -111,4 +116,30 @@ protected SessionVariable findConfigFromGlobalSessionVar(String varName) throws
         now = "23:30:00";
         Assertions.assertFalse(StatisticsUtil.inAnalyzeTime(LocalTime.parse(now, timeFormatter)));
     }
+
+
+    @Test
+    public void testEncodeValue() throws Exception {
+        Assertions.assertEquals("NULL", StatisticsUtil.encodeValue(null, 0));
+
+        ResultRow row = new ResultRow(null);
+        Assertions.assertEquals("NULL", StatisticsUtil.encodeValue(row, 0));
+
+        ArrayList<String> values = Lists.newArrayList();
+        values.add("a");
+        row = new ResultRow(values);
+        Assertions.assertEquals("NULL", StatisticsUtil.encodeValue(row, 1));
+
+        values = Lists.newArrayList();
+        values.add(null);
+        row = new ResultRow(values);
+        Assertions.assertEquals("NULL", StatisticsUtil.encodeValue(row, 0));
+
+        values.add("a");
+        row = new ResultRow(values);
+        Assertions.assertEquals("NULL", StatisticsUtil.encodeValue(row, 0));
+        Assertions.assertEquals(Base64.getEncoder()
+                .encodeToString("a".getBytes(StandardCharsets.UTF_8)), StatisticsUtil.encodeValue(row, 1));
+        Assertions.assertEquals("NULL", StatisticsUtil.encodeValue(row, 2));
+    }
 }