EXPLAIN FORMAT=JSON

Add support for semi-join strategies: FirstMatch, DuplicateWeedout,
LooseScan.

3 files changed, 32 insertions, 3 deletions

diff --git a/sql/sql_explain.cc b/sql/sql_explain.cc
index c4f8002494f..7e6c1c6cf5c 100644
--- a/sql/sql_explain.cc
+++ b/sql/sql_explain.cc
@@ -732,7 +732,13 @@ void Explain_basic_join::print_explain_json(Explain_query *query,
   writer->add_member("select_id").add_ll(select_id);
   for (uint i=0; i< n_join_tabs; i++)
   {
+    if (join_tabs[i]->start_dups_weedout)
+      writer->add_member("duplicates_removal").start_object();
+    
     join_tabs[i]->print_explain_json(query, writer, is_analyze);
+    
+    if (join_tabs[i]->end_dups_weedout)
+      writer->end_object();
   }
   print_explain_json_for_children(query, writer, is_analyze);
   writer->end_object();
@@ -1089,9 +1095,7 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
       write_item(writer, pushed_index_cond);
       break;
     case ET_USING_WHERE:
-      if (where_cond)
       {
-        writer->add_member("attached_condition");
         /*
           We are printing the condition that is checked when scanning this
           table.
@@ -1099,7 +1103,11 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
           - in other cases, it is where_cond.
         */
         Item *item= bka_type.is_using_jbuf()? cache_cond: where_cond;
-        write_item(writer, item);
+        if (item)
+        {
+          writer->add_member("attached_condition");
+          write_item(writer, item);
+        }
       }
       break;
     case ET_USING_INDEX:
@@ -1110,6 +1118,15 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
       break;
     case ET_USING_JOIN_BUFFER:
       /* Do nothing. Join buffer is handled differently */
+    case ET_START_TEMPORARY:
+    case ET_END_TEMPORARY:
+      /* Handled as "duplicates_removal: { ... } */
+      break;
+    case ET_FIRST_MATCH:
+      writer->add_member("first_match").add_str(firstmatch_table_name.c_ptr());
+      break;
+    case ET_LOOSESCAN:
+      writer->add_member("loose_scan").add_bool(true);
       break;
     default:
       DBUG_ASSERT(0);
diff --git a/sql/sql_explain.h b/sql/sql_explain.h
index 20e2f856840..68ef59c732d 100644
--- a/sql/sql_explain.h
+++ b/sql/sql_explain.h
@@ -539,6 +539,8 @@ public:
   Explain_table_access() :
     derived_select_number(0),
     non_merged_sjm_number(0),
+    start_dups_weedout(false),
+    end_dups_weedout(false),
     where_cond(NULL),
     cache_cond(NULL),
     pushed_index_cond(NULL),
@@ -615,6 +617,9 @@ public:
   EXPLAIN_BKA_TYPE bka_type;
   
   StringBuffer<32> firstmatch_table_name;
+
+  bool start_dups_weedout;
+  bool end_dups_weedout;
   
   /*
     Note: lifespan of WHERE condition is less than lifespan of this object.
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 511e7106bd5..985b743eaad 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -23641,9 +23641,16 @@ void JOIN_TAB::save_explain_data(Explain_table_access *eta, table_map prefix_tab
     }
 
     if (tab->first_weedout_table)
+    {
+      eta->start_dups_weedout= true;
       eta->push_extra(ET_START_TEMPORARY);
+    }
     if (tab->check_weed_out_table)
+    {
       eta->push_extra(ET_END_TEMPORARY);
+      eta->end_dups_weedout= true;
+    }
+
     else if (tab->do_firstmatch)
     {
       if (tab->do_firstmatch == /*join->join_tab*/ first_top_tab - 1)