MWL#182: Explain running statements

- Get subqueries to work, part #1.

2 files changed, 26 insertions, 2 deletions

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 9aee5caeb64..3b355a312af 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -3706,6 +3706,22 @@ int st_select_lex::print_explain(select_result_sink *output)
                              FALSE, // bool need_order,
                              FALSE, // bool distinct,
                              NULL); //const char *message
+    if (res)
+      goto err;
+
+    for (SELECT_LEX_UNIT *unit= join->select_lex->first_inner_unit();
+         unit;
+         unit= unit->next_unit())
+    {
+      /* 
+        Display subqueries only if they are not parts of eliminated WHERE/ON
+        clauses.
+      */
+      if (!(unit->item && unit->item->eliminated))
+      {
+        unit->print_explain(output);
+      }
+    }
   }
   else
   {
@@ -3717,6 +3733,7 @@ int st_select_lex::print_explain(select_result_sink *output)
                              FALSE, // bool distinct,
                              msg); //const char *message
   }
+err:
   return 0;
 }
 
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 4dc99cf006c..fcbd2615b9c 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -265,7 +265,9 @@ void dbug_serve_apcs(THD *thd, int n_calls)
 
 
 /*
-  Usage
+  Debugging: check if @name=value, comparing as integer
+
+  Intended usage:
   
   DBUG_EXECUTE_IF("show_explain_probe_2", 
                      if (dbug_user_var_equals_int(thd, "select_id", select_id)) 
@@ -2102,7 +2104,6 @@ void JOIN::exec_inner()
   int      tmp_error;
   DBUG_ENTER("JOIN::exec");
   
-  DBUG_EXECUTE_IF("show_explain_probe_2", dbug_serve_apcs(thd, 1););
   DBUG_EXECUTE_IF("show_explain_probe_1", 
                   if (dbug_user_var_equals_int(thd, 
                                                "show_explain_probe_select_id", 
@@ -20516,6 +20517,7 @@ void JOIN::clear()
   }
 }
 
+
 int print_fake_select_lex_join(select_result_sink *result, bool on_the_fly,
                                SELECT_LEX *select_lex, uint8 select_options)
 {
@@ -20594,6 +20596,7 @@ int print_fake_select_lex_join(select_result_sink *result, bool on_the_fly,
   return 0;
 }
 
+
 /**
   EXPLAIN handling.
 
@@ -21162,6 +21165,10 @@ int JOIN::print_explain(select_result_sink *result, bool on_the_fly,
 }
 
 
+/*
+  See st_select_lex::print_explain() for the SHOW EXPLAIN counterpart
+*/ 
+
 static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 			    bool distinct,const char *message)
 {