1 files changed, 72 insertions, 0 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index cc4b139fb2f..a48eff66386 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -23972,6 +23972,78 @@ uint get_index_for_order(ORDER *order, TABLE *table, SQL_SELECT *select,
   return MAX_KEY;
 }
 
+/*
+  Count how much times conditions are true for several first rows of the table
+
+  @param thd             thread handle
+  @param rows_to_read    how much rows to check
+  @param table           table which should be checked
+  @conds conds           list of conditions and countars for them
+
+  @return number of really checked rows or 0 in case of error or empty table
+*/
+
+ulong check_selectivity(THD *thd,
+                        ulong rows_to_read,
+                        TABLE *table,
+                        List<COND_STATISTIC> *conds)
+{
+  ulong count= 0;
+  COND_STATISTIC *cond;
+  List_iterator_fast<COND_STATISTIC> it(*conds);
+  handler *file= table->file;
+  uchar *record= table->record[0];
+  int error= 0;
+  DBUG_ENTER("check_selectivity");
+
+  DBUG_ASSERT(rows_to_read > 0);
+  while ((cond= it++))
+  {
+    DBUG_ASSERT(cond->cond);
+    DBUG_ASSERT(cond->cond->used_tables() == table->map);
+    cond->positive= 0;
+  }
+  it.rewind();
+
+  if (file->ha_rnd_init_with_error(1))
+    DBUG_RETURN(0);
+  do
+  {
+    error= file->ha_rnd_next(record);
+
+    if (thd->killed)
+    {
+      thd->send_kill_message();
+      count= 0;
+      goto err;
+    }
+    if (error)
+    {
+      if (error == HA_ERR_RECORD_DELETED)
+        continue;
+      if (error == HA_ERR_END_OF_FILE)
+	break;
+      goto err;
+    }
+
+    count++;
+    while ((cond= it++))
+    {
+      if (cond->cond->val_bool())
+        cond->positive++;
+    }
+    it.rewind();
+
+  } while (count < rows_to_read);
+
+  file->ha_rnd_end();
+  DBUG_RETURN(count);
+
+err:
+  DBUG_PRINT("error", ("error %d", error));
+  file->ha_rnd_end();
+  DBUG_RETURN(0);
+}
 
 /**
   @} (end of group Query_Optimizer)