add comment for ignore float/double when compute hash code

Author: marising

be/src/olap/row.h

@@ -189,7 +189,9 @@ uint32_t hash_row(const RowType& row, uint32_t seed) {
     FieldType type;
     for (uint32_t cid : row.schema()->column_ids()) {
         type = row.schema()->column(cid)->type();
-        if (type == OLAP_FIELD_TYPE_FLOAT || type == OLAP_FIELD_TYPE_DOUBLE) {
+        //The approximation of float/double in a certain precision range, the binary of byte is not
+        //a fixed value, so these two types are ignored in calculating hash code.
+	    if (type == OLAP_FIELD_TYPE_FLOAT || type == OLAP_FIELD_TYPE_DOUBLE) {
             continue;
         }
         seed = row.schema()->column(cid)->hash_code(row.cell(cid), seed);