Fix bug lp:827416

Analysis:
Constant table optimization of the outer query finds that
the right side of the equality is a constant that can
be used for an eq_ref access to fetch one row from t1,
and substitute t1 with a constant. Thus constant optimization
triggers evaluation of the subquery during the optimize
phase of the outer query.

The innermost subquery requires a plan with a temporary
table because with InnoDB tables the exact count of rows
is not known, and the empty tables cannot be optimzied
way. JOIN::exec for the innermost subquery substitutes
the subquery tables with a temporary table.

When EXPLAIN gets to print the tables in the innermost
subquery, EXPLAIN needs to print the name of each table
through the corresponding TABLE_LIST object. However,
the temporary table created during execution doesn't
have a corresponding TABLE_LIST, so we get a null
pointer exception.

Solution:
The solution is to forbid using expensive constant
expressions for eq_ref access for contant table
optimization. Notice that eq_ref with a subquery
providing the value is still possible during regular
execution.

1 files changed, 7 insertions, 0 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 6d2c7400d3d..54c1215164e 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -2993,6 +2993,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
   uint i,table_count,const_count,key;
   table_map found_const_table_map, all_table_map, found_ref, refs;
   key_map const_ref, eq_part;
+  bool has_expensive_keyparts;
   TABLE **table_vector;
   JOIN_TAB *stat,*stat_end,*s,**stat_ref;
   KEYUSE *keyuse,*start_keyuse;
@@ -3314,12 +3315,17 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
 	  refs=0;
           const_ref.clear_all();
 	  eq_part.clear_all();
+          has_expensive_keyparts= false;
 	  do
 	  {
 	    if (keyuse->val->type() != Item::NULL_ITEM && !keyuse->optimize)
 	    {
 	      if (!((~found_const_table_map) & keyuse->used_tables))
+              {
 		const_ref.set_bit(keyuse->keypart);
+                if (keyuse->val->is_expensive())
+                  has_expensive_keyparts= true;
+              }
 	      else
 		refs|=keyuse->used_tables;
 	      eq_part.set_bit(keyuse->keypart);
@@ -3341,6 +3347,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
             if (table->key_info[key].flags & HA_NOSAME)
             {
 	      if (const_ref == eq_part &&
+                  !has_expensive_keyparts &&
                   !((outer_join & table->map) &&
                     (*s->on_expr_ref)->is_expensive()))
 	      {					// Found everything for ref.