Fix bugs in MinMaxDataMap

make minmax datamap useable and add more tests for it

core/src/main/java/org/apache/carbondata/core/datastore/page/statistics/DummyStatsCollector.java

@@ -48,6 +48,10 @@ public class DummyStatsCollector implements ColumnPageStatsCollector {
       return BYTE_ARRAY;
     }
 
+    @Override
+    public void clear() {
+
+    }
   };
 
   @Override public void updateNull(int rowId) {

core/src/main/java/org/apache/carbondata/core/datastore/page/statistics/KeyPageStatsCollector.java

@@ -107,6 +107,11 @@ public SimpleStatsResult getPageStats() {
         return dataType;
       }
 
+      @Override
+      public void clear() {
+        min = null;
+        max = null;
+      }
     };
   }
 }

core/src/main/java/org/apache/carbondata/core/datastore/page/statistics/LVStringStatsCollector.java

@@ -105,6 +105,11 @@ public SimpleStatsResult getPageStats() {
         return DataTypes.STRING;
       }
 
+      @Override
+      public void clear() {
+        min = null;
+        max = null;
+      }
     };
   }
 }

core/src/main/java/org/apache/carbondata/core/datastore/page/statistics/PrimitivePageStatsCollector.java

@@ -120,6 +120,10 @@ public static PrimitivePageStatsCollector newInstance(ValueEncoderMeta meta) {
 
   private PrimitivePageStatsCollector(DataType dataType) {
     this.dataType = dataType;
+    resetPageStats();
+  }
+
+  private void resetPageStats() {
     if (dataType == DataTypes.BOOLEAN) {
       minByte = TRUE_VALUE;
       maxByte = FALSE_VALUE;
@@ -343,4 +347,8 @@ public DataType getDataType() {
     return dataType;
   }
 
+  @Override
+  public void clear() {
+    resetPageStats();
+  }
 }

core/src/main/java/org/apache/carbondata/core/datastore/page/statistics/SimpleStatsResult.java

@@ -29,4 +29,8 @@ public interface SimpleStatsResult {
 
   DataType getDataType();
 
+  /**
+   * clear the statistics info for resuse
+   */
+  void clear();
 }