Code cleanup

mysql-test/r/explain_non_select.result

@@ -102,3 +102,15 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	8	Using where
 1	SIMPLE	t1	ref	a	a	5	test.t0.a	4	Using index
 drop table t0, t1;
+#
+# Try DELETE ... RETURNING ...
+#
+create table t0 (a int);
+insert into t0 values (1),(2),(3),(4);
+explain delete from t0 where a=1 returning a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	4	Using where
+explain delete from t0 returning a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	4	
+drop table t0;

sql/opt_qpf.cc

@@ -14,8 +14,6 @@ QPF_query::QPF_query()
 {
   upd_del_plan= NULL;
   operations= 0;
-  //memset(&unions, 0, sizeof(unions));
-  //memset(&selects, 0, sizeof(selects));
 }
 
 
@@ -105,18 +103,13 @@ int QPF_query::print_explain(select_result_sink *output,
   }
   else
   {
-    // Start with id=1
+    // Start printing from id=1
     QPF_node *node= get_node(1);
     return node->print_explain(this, output, explain_flags);
   }
 }
 
 
-void QPF_union::push_table_name(List<Item> *item_list)
-{
-}
-
-
 static void push_str(List<Item> *item_list, const char *str)
 {
   item_list->push_back(new Item_string(str,
@@ -134,7 +127,7 @@ static void push_string(List<Item> *item_list, String *str)
 int QPF_union::print_explain(QPF_query *query, select_result_sink *output, 
                              uint8 explain_flags)
 {
-  // print all children, in order
+  /* print all UNION children, in order */
   for (int i= 0; i < (int) union_members.elements(); i++)
   {
     QPF_select *sel= query->get_select(union_members.at(i));
@@ -152,7 +145,6 @@ int QPF_union::print_explain(QPF_query *query, select_result_sink *output,
   push_str(&item_list, fake_select_type);
 
   /* `table` column: something like "<union1,2>" */
-  //
   {
     char table_name_buffer[SAFE_NAME_LEN];
     uint childno= 0;
@@ -180,8 +172,6 @@ int QPF_union::print_explain(QPF_query *query, select_result_sink *output,
     const CHARSET_INFO *cs= system_charset_info;
     item_list.push_back(new Item_string(table_name_buffer, len, cs));
   }
-  //
-  push_table_name(&item_list);
   
   /* `partitions` column */
   if (explain_flags & DESCRIBE_PARTITIONS)
@@ -221,11 +211,19 @@ int QPF_union::print_explain(QPF_query *query, select_result_sink *output,
   //output->unit.offset_limit_cnt= 0; 
   if (output->send_data(item_list))
     return 1;
-
+  
+  /*
+    Print all subquery children (UNION children have already been printed at
+    the start of this function)
+  */
   return print_explain_for_children(query, output, explain_flags);
 }
 
 
+/*
+  Print EXPLAINs for all children nodes (i.e. for subqueries)
+*/
+
 int QPF_node::print_explain_for_children(QPF_query *query, 
                                          select_result_sink *output,
                                          uint8 explain_flags)
@@ -301,6 +299,12 @@ int QPF_select::print_explain(QPF_query *query, select_result_sink *output,
 }
 
 
+void QPF_table_access::push_extra(enum Extra_tag extra_tag)
+{
+  extra_tags.append(extra_tag);
+}
+
+
 int QPF_table_access::print_explain(select_result_sink *output, uint8 explain_flags, 
                                     uint select_id, const char *select_type,
                                     bool using_temporary, bool using_filesort)
@@ -422,13 +426,17 @@ int QPF_table_access::print_explain(select_result_sink *output, uint8 explain_fl
 }
 
 
+/*
+  Elements in this array match members of enum Extra_tag, defined in opt_qpf.h.
+*/
+
 const char * extra_tag_text[]=
 {
   "ET_none",
   "Using index condition",
   "Using index condition(BKA)",
-  "Using ", //special
-  "Range checked for each record (index map: 0x", //special
+  "Using ", // special handling
+  "Range checked for each record (index map: 0x", // special handling
   "Using where with pushed condition",
   "Using where",
   "Not exists",
@@ -443,17 +451,17 @@ const char * extra_tag_text[]=
   "Scanned 1 database",
   "Scanned all databases",
 
-  "Using index for group-by", // Special?
+  "Using index for group-by", // special handling
 
-  "USING MRR: DONT PRINT ME", // Special!
+  "USING MRR: DONT PRINT ME", // special handling
 
   "Distinct",
   "LooseScan",
   "Start temporary",
   "End temporary",
-  "FirstMatch", //TODO: also handle special variant!
+  "FirstMatch", // special handling
 
-  "Using join buffer", // Special!,
+  "Using join buffer", // special handling 
 
   "const row not found",
   "unique row not found",

sql/opt_qpf.h

@@ -146,7 +146,6 @@ class QPF_union : public QPF_node
   {
     union_members.append(select_no);
   }
-  void push_table_name(List<Item> *item_list);
   int print_explain(QPF_query *query, select_result_sink *output, 
                     uint8 explain_flags);
 
@@ -231,6 +230,11 @@ class QPF_query : public Sql_alloc
 };
 
 
+/* 
+  Some of the tags have matching text. See extra_tag_text for text names, and 
+  QPF_table_access::append_tag_name() for code to convert from tag form to text
+  form.
+*/
 enum Extra_tag
 {
   ET_none= 0, /* not-a-tag */
@@ -347,7 +351,6 @@ class QPF_table_access : public Sql_alloc
   StringBuffer<64> mrr_type;
 
   // valid with ET_USING_JOIN_BUFFER
-  //StringBuffer<64> join_buffer_type;
   QPF_BKA_TYPE bka_type;
   
   //TABLE *firstmatch_table;

sql/sql_select.cc

@@ -11172,7 +11172,7 @@ void JOIN::cleanup(bool full)
   if (full)
   {
     /* Save it again */
-#if 0    
+#if 0    psergey-todo: remove?
     if (select_lex->select_number != UINT_MAX && 
         select_lex->select_number != INT_MAX /* this is not a UNION's "fake select */ && 
         have_query_plan != QEP_NOT_PRESENT_YET && 
@@ -22487,11 +22487,7 @@ void explain_append_mrr_info(QUICK_RANGE_SELECT *quick, String *res)
 }
 
 
-/////////////////////////////////////////////////////////////////////////////////////////////////
-void QPF_table_access::push_extra(enum Extra_tag extra_tag)
-{
-  extra_tags.append(extra_tag);
-}
+///////////////////////////////////////////////////////////////////////////////
 
 void append_possible_keys(String *str, TABLE *table, key_map possible_keys)
 {
@@ -22548,24 +22544,7 @@ int JOIN::save_qpf(QPF_query *output, bool need_tmp_table, bool need_order,
   }
   else if (join->select_lex == join->unit->fake_select_lex)
   {
-#if 0
-    select_lex->set_explain_type(on_the_fly);
-    QPF_union *qp_union= new (output->mem_root) QPF_union;
-    qp_node= qp_union;
-
-    SELECT_LEX *child;
-    for (child= select_lex->master_unit()->first_select(); child;
-         child=child->next_select())
-    {
-      qp_union->add_select(child->select_number);
-    }
-
-    qp_union->fake_select_type= select_lex->type;
-    qp_union->using_filesort=
-      test(select_lex->master_unit()->global_parameters->order_list.first);
-
-    output->add_node(qp_union);
-#endif    
+    /* Do nothing, QPF_union will create and print fake_select_lex */
   }
   else if (!join->select_lex->master_unit()->derived ||
            join->select_lex->master_unit()->derived->is_materialized_derived())
@@ -22713,7 +22692,7 @@ int JOIN::save_qpf(QPF_query *output, bool need_tmp_table, bool need_order,
 
       // tmp2 holds key_name
       // tmp3 holds key_length
-      // tmp4 holds ref?
+      // tmp4 holds ref
       if (tab_type == JT_NEXT)
       {
 	key_info= table->key_info+tab->index;
@@ -23074,16 +23053,16 @@ int JOIN::save_qpf(QPF_query *output, bool need_tmp_table, bool need_order,
 
 
 /*
-  This function servers as "shortcut point" for EXPLAIN queries.
-
-  For UNIONs and JOINs, EXPLAIN statement executes just like its SELECT
-  statement would execute, except that JOIN::exec() will call select_describe()
-  instead of actually executing the query.
+  This function serves as "shortcut point" for EXPLAIN queries.
+  
+  The EXPLAIN statement executes just like its SELECT counterpart would
+  execute, except that JOIN::exec() will call select_describe() instead of
+  actually executing the query.
 
-  The purpose of select_describe() is:
-  - update the query plan with info about last-minute choices made at the start
-    of JOIN::exec
-  - Invoke "pseudo-execution" for the children subqueries.
+  Inside select_describe():
+  - Query plan is updated with latest QEP choices made at the start of
+    JOIN::exec().
+  - the proces of "almost execution" is invoked for the children subqueries.
 
   Overall, select_describe() is a legacy of old EXPLAIN implementation and
   should be removed.
@@ -23096,9 +23075,10 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
   select_result *result=join->result;
   DBUG_ENTER("select_describe");
   
-  // Update the QPF:
+  /* Update the QPF with latest values of using_temporary, using_filesort */
   QPF_select *qp;
-  if ((qp= thd->lex->query_plan_footprint->get_select(join->select_lex->select_number)))
+  uint select_nr= join->select_lex->select_number;
+  if ((qp= thd->lex->query_plan_footprint->get_select(select_nr)))
   {
     qp->using_temporary= need_tmp_table;
     qp->using_filesort= need_order;

sql/sql_select.h

@@ -259,7 +259,6 @@ typedef struct st_join_table {
   
   /* Special content for EXPLAIN 'Extra' column or NULL if none */
   enum Extra_tag info;
-  //const char	*info;
 
   /* 
     Bitmap of TAB_INFO_* bits that encodes special line for EXPLAIN 'Extra'