Implementation of WL#2486 -

"Process NATURAL and USING joins according to SQL:2003".

* Some of the main problems fixed by the patch:
  - in "select *" queries the * expanded correctly according to
    ANSI for arbitrary natural/using joins
  - natural/using joins are correctly transformed into JOIN ... ON
    for any number/nesting of the joins.
  - column references are correctly resolved against natural joins
    of any nesting and combined with arbitrary other joins.

* This patch also contains a fix for name resolution of items
  inside the ON condition of JOIN ... ON - in this case items must
  be resolved only against the JOIN operands. To support such
  'local' name resolution, the patch introduces a stack of
  name resolution contexts used at parse time.

NOTICE:
- This patch is not complete in the sense that
  - there are 2 test cases that still do not pass -
    one in join.test, one in select.test. Both are marked
    with a comment "TODO: WL#2486".
  - it does not include a new test specific for the task


mysql-test/include/ps_query.inc:
  Adjusted according to standard NATURAL/USING join semantics.,
mysql-test/r/bdb.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/derived.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/errors.result:
  The column as a whole cannot be resolved, so different error message.
mysql-test/r/fulltext.result:
  Adjusted according to standard JOIN ... ON semantics =>
  the ON condition can refer only to the join operands.
mysql-test/r/fulltext_order_by.result:
  More detailed error message.
mysql-test/r/innodb.result:
  Adjusted according to standard NATURAL/USING join semantics.
  This test doesn't pass completetly yet!
mysql-test/r/insert_select.result:
  More detailed error message.
mysql-test/r/join.result:
  Adjusted according to standard NATURAL/USING join semantics.
  
  NOTICE: there is one test case that still fails, and it is
  commeted out and marked with WL#2486 in the test file.
mysql-test/r/join_crash.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/join_nested.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/join_outer.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/multi_update.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/null_key.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/order_by.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/ps_2myisam.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/ps_3innodb.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/ps_4heap.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/ps_5merge.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/ps_6bdb.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/ps_7ndb.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/select.result:
  Adjusted according to standard NATURAL/USING join semantics.
  
  NOTICE: there is one failing test case which is commented with
  WL#2486 in the test file.
mysql-test/r/subselect.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/type_ranges.result:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/r/union.result:
  More detailed error message.
mysql-test/t/bdb.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/errors.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/fulltext.test:
  Adjusted according to standard JOIN ... ON semantics =>
  the ON condition can refer only to the join operands.
mysql-test/t/fulltext_order_by.test:
  More detailed error message.
mysql-test/t/innodb.test:
  Adjusted according to standard NATURAL/USING join semantics.
  This test doesn't pass completetly yet!
mysql-test/t/insert_select.test:
  More detailed error message.
mysql-test/t/join.test:
  Adjusted according to standard NATURAL/USING join semantics.
  
  NOTICE: there is one test case that still fails, and it is
  commeted out and marked with WL#2486 in the test file.
mysql-test/t/join_crash.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/join_nested.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/join_outer.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/null_key.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/order_by.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/select.test:
  Adjusted according to standard NATURAL/USING join semantics.
  
  NOTICE: there is one test case that still fails, and it is
  commeted out and marked with WL#2486 in the test file.
mysql-test/t/subselect.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/type_ranges.test:
  Adjusted according to standard NATURAL/USING join semantics.
mysql-test/t/union.test:
  More detailed error message.
sql/item.cc:
  - extra parameter to find_field_in_tables
  - find_field_in_real_table renamed to find_field_in_table
  - fixed comments/typos
sql/item.h:
  - added [first | last]_name_resolution_table to class
    Name_resolution_context
  - commented old code
  - standardized formatting
sql/mysql_priv.h:
  - refactored the find_field_in_XXX procedures,
  - added a new procedure for natural join table references,
  - renamed the find_field_in_XXX procedures to clearer names
sql/sp.cc:
  - pass the top-most list of the FROM clause to setup_tables
  - extra parameter to find_field_in_tables
sql/sql_acl.cc:
  - renamed find_field_in_table => find_field_in_table_ref
  - extra parameter to find_field_in_table_ref
  - commented old code
sql/sql_base.cc:
  This file contains the core of the implementation of the processing
  of NATURAL/USING joins (WL#2486).
  - added many comments to old code
  - refactored the group of find_field_in_XXX procedures, and added a
    new procedure for natural joins. There is one find_field_in_XXX procedure
    per each type of table reference (stored table, merge view, or natural
    join); one meta-procedure that selects the correct one depeneding on the
    table reference; and one procedure that goes over a list of table
    referenes.
  - NATURAL/USING joins are processed through the procedures:
      mark_common_columns, store_natural_using_join_columns,
      store_top_level_join_columns, setup_natural_join_row_types.
    The entry point to processing NATURAL/USING joins is the
    procedure 'setup_natural_join_row_types'.
  - Replaced the specialized Field_iterator_XXX iterators with one
    generic iterator over the fields of a table reference.
  - Simplified 'insert_fields' and 'setup_conds' due to encapsulation of
    the processing of natural joins in a separate set of procedures.
sql/sql_class.h:
  - Commented old code.
sql/sql_delete.cc:
  - Pass the FROM clause to setup_tables.
sql/sql_help.cc:
  - pass the end name resolution table to find_field_in_tables
  - adjust the list of tables for name resolution
sql/sql_insert.cc:
  - Changed the code that saves and restores the current context to
    support the list of tables for name resolution -
    context->first_name_resolution_table, and
    table_list->next_name_resolution_table.
    Needed to support an ugly trick to resolve inserted columns only in
    the first table.
  - Added Name_resolution_context::[first | last]_name_resolution_table.
  - Commented old code
sql/sql_lex.cc:
  - set select_lex.parent_lex correctly
  - set correct state of the current name resolution context
sql/sql_lex.h:
  - Added a stack of name resolution contexts to support local
    contexts for JOIN ... ON conditions.
  - Commented old code.
sql/sql_load.cc:
  - Pass the FROM clause to setup_tables.
sql/sql_olap.cc:
  - Pass the FROM clause to setup_tables.
sql/sql_parse.cc:
  - correctly set SELECT_LEX::parent_lex
  - set the first table of the current name resoltion context
  - added support for NATURAL/USING joins
  - commented old code
sql/sql_select.cc:
  - Pass the FROM clause to setup_tables.
  - Pass the end table to find_field_in_tables
  - Improved comments
sql/sql_show.cc:
  - Set SELECT_LEX::parent_lex.
sql/sql_update.cc:
  - Pass the FROM clause to setup_tables.
sql/sql_yacc.yy:
  - Added support for a stack of name resolution contexts needed to
    implement name resolution for JOIN ... ON. A context is pushed
    for each new JOIN ... ON, and popped afterwards.
  - Added support for NATURAL/USING joins.
sql/table.cc:
  - Added new class Natural_join_column to hide the heterogeneous
    representation of column references for stored tables and for
    views.
  - Added a new list TABLE_LIST::next_name_resolution_table to
    support name resolution with NATURAL/USING joins. Also added
    other members to TABLE_LIST to support NATURAL/USING joins.
  - Added a generic iterator over the fields of table references
    of various types - class Field_iterator_table_ref
sql/table.h:
  - Added new class Natural_join_column to hide the heterogeneous
    representation of column references for stored tables and for
    views.
  - Added a new list TABLE_LIST::next_name_resolution_table to
    support name resolution with NATURAL/USING joins. Also added
    other members to TABLE_LIST to support NATURAL/USING joins.
  - Added a generic iterator over the fields of table references
    of various types - class Field_iterator_table_ref
tests/mysql_client_test.c:
  Adjusted according to standard NATURAL JOIN syntax.

1 files changed, 123 insertions, 68 deletions

diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index b680787b9a3..d5d0ac8fff0 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -717,7 +717,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 	bool_term bool_factor bool_test bool_pri 
 	predicate bit_expr bit_term bit_factor value_expr term factor
 	table_wild simple_expr udf_expr
-	using_list expr_or_default set_expr_or_default interval_expr
+	expr_or_default set_expr_or_default interval_expr
 	param_marker singlerow_subselect singlerow_subselect_init
 	exists_subselect exists_subselect_init geometry_function
 	signed_literal now_or_signed_literal opt_escape
@@ -739,7 +739,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 	key_alg opt_btree_or_rtree
 
 %type <string_list>
-	key_usage_list
+	key_usage_list using_list
 
 %type <key_part>
 	key_part
@@ -4420,10 +4420,10 @@ simple_expr:
 	      my_error(ER_WRONG_COLUMN_NAME, MYF(0), name->str);
 	      YYABORT;
 	    }
-	    $$= new Item_default_value(&Select->context, $3);
+	    $$= new Item_default_value(Lex->current_context(), $3);
 	  }
 	| VALUES '(' simple_ident ')'
-	  { $$= new Item_insert_value(&Select->context, $3); }
+	  { $$= new Item_insert_value(Lex->current_context(), $3); }
 	| FUNC_ARG0 '(' ')'
 	  {
 	    if (!$1.symbol->create_func)
@@ -4714,9 +4714,9 @@ simple_expr:
 	    name->init_qname(YYTHD);
 	    sp_add_used_routine(lex, YYTHD, name, TYPE_ENUM_FUNCTION);
 	    if ($5)
-	      $$= new Item_func_sp(&lex->current_select->context, name, *$5);
+	      $$= new Item_func_sp(Lex->current_context(), name, *$5);
 	    else
-	      $$= new Item_func_sp(&lex->current_select->context, name);
+	      $$= new Item_func_sp(Lex->current_context(), name);
 	    lex->safe_to_cache_query=0;
 	  }
 	| IDENT_sys '(' udf_expr_list ')'
@@ -4804,9 +4804,9 @@ simple_expr:
 
               sp_add_used_routine(lex, YYTHD, name, TYPE_ENUM_FUNCTION);
               if ($3)
-                $$= new Item_func_sp(&lex->current_select->context, name, *$3);
+                $$= new Item_func_sp(Lex->current_context(), name, *$3);
               else
-                $$= new Item_func_sp(&lex->current_select->context, name);
+                $$= new Item_func_sp(Lex->current_context(), name);
 	      lex->safe_to_cache_query=0;
 	    }
           }
@@ -5010,7 +5010,7 @@ sum_expr:
 	  {
             SELECT_LEX *sel= Select;
 	    sel->in_sum_expr--;
-	    $$=new Item_func_group_concat(&sel->context, $3, $5,
+	    $$=new Item_func_group_concat(Lex->current_context(), $3, $5,
                                           sel->gorder_list, $7);
 	    $5->empty();
 	  };
@@ -5146,68 +5146,116 @@ join_table:
         table_ref normal_join table_ref { YYERROR_UNLESS($1 && ($$=$3)); }
 	| table_ref STRAIGHT_JOIN table_factor
 	  { YYERROR_UNLESS($1 && ($$=$3)); $3->straight=1; }
-	| table_ref normal_join table_ref ON expr
-	  { YYERROR_UNLESS($1 && ($$=$3)); add_join_on($3,$5); }
-        | table_ref STRAIGHT_JOIN table_factor ON expr
-          { YYERROR_UNLESS($1 && ($$=$3)); $3->straight=1; add_join_on($3,$5); }
+	| table_ref normal_join table_ref
+          ON
+          {
+            YYERROR_UNLESS($1 && ($$=$3));
+            /* Change the current name resolution context to a local context. */
+            Name_resolution_context *on_context;
+            if (!(on_context= make_join_on_context(YYTHD,$1,$3)))
+              YYABORT;
+            Lex->push_context(on_context);
+          }
+          expr
+	  {
+            add_join_on($3,$6);
+            Lex->pop_context();
+          }
+        | table_ref STRAIGHT_JOIN table_factor
+          ON
+          {
+            YYERROR_UNLESS($1 && ($$=$3));
+            /* Change the current name resolution context to a local context. */
+            Name_resolution_context *on_context;
+            if (!(on_context= make_join_on_context(YYTHD,$1,$3)))
+              YYABORT;
+            Lex->push_context(on_context);
+          }
+          expr
+          {
+            $3->straight=1;
+            add_join_on($3,$6);
+            Lex->pop_context();
+          }
 	| table_ref normal_join table_ref
 	  USING
 	  {
 	    SELECT_LEX *sel= Select;
             YYERROR_UNLESS($1 && $3);
-            sel->save_names_for_using_list($1, $3);
 	  }
 	  '(' using_list ')'
-	  { add_join_on($3,$7); $$=$3; }
-
-	| table_ref LEFT opt_outer JOIN_SYM table_ref ON expr
-	  { YYERROR_UNLESS($1 && $5); add_join_on($5,$7); $5->outer_join|=JOIN_TYPE_LEFT; $$=$5; }
+          { add_join_natural($1,$3,$7); $$=$3; }
+	| table_ref LEFT opt_outer JOIN_SYM table_ref
+          ON
+          {
+            /* Change the current name resolution context to a local context. */
+            Name_resolution_context *on_context;
+            if (!(on_context= make_join_on_context(YYTHD,$1,$5)))
+              YYABORT;
+            Lex->push_context(on_context);
+          }
+          expr
+	  {
+            YYERROR_UNLESS($1 && $5);
+            add_join_on($5,$8);
+            Lex->pop_context();
+            $5->outer_join|=JOIN_TYPE_LEFT;
+            $$=$5;
+          }
 	| table_ref LEFT opt_outer JOIN_SYM table_factor
 	  {
 	    SELECT_LEX *sel= Select;
             YYERROR_UNLESS($1 && $5);
-            sel->save_names_for_using_list($1, $5);
 	  }
 	  USING '(' using_list ')'
-	  { add_join_on($5,$9); $5->outer_join|=JOIN_TYPE_LEFT; $$=$5; }
+          { add_join_natural($1,$5,$9); $5->outer_join|=JOIN_TYPE_LEFT; $$=$5; }
 	| table_ref NATURAL LEFT opt_outer JOIN_SYM table_factor
 	  {
             YYERROR_UNLESS($1 && $6);
-	    add_join_natural($1,$6);
+ 	    add_join_natural($1,$6,NULL);
 	    $6->outer_join|=JOIN_TYPE_LEFT;
 	    $$=$6;
 	  }
-	| table_ref RIGHT opt_outer JOIN_SYM table_ref ON expr
+	| table_ref RIGHT opt_outer JOIN_SYM table_ref
+          ON
+          {
+            /* Change the current name resolution context to a local context. */
+            Name_resolution_context *on_context;
+            if (!(on_context= make_join_on_context(YYTHD,$1,$5)))
+              YYABORT;
+            Lex->push_context(on_context);
+          }
+          expr
           {
 	    LEX *lex= Lex;
             YYERROR_UNLESS($1 && $5);
             if (!($$= lex->current_select->convert_right_join()))
               YYABORT;
-            add_join_on($$, $7);
+            add_join_on($$, $8);
+            Lex->pop_context();
           }
 	| table_ref RIGHT opt_outer JOIN_SYM table_factor
 	  {
 	    SELECT_LEX *sel= Select;
             YYERROR_UNLESS($1 && $5);
-            sel->save_names_for_using_list($1, $5);
 	  }
 	  USING '(' using_list ')'
           {
 	    LEX *lex= Lex;
             if (!($$= lex->current_select->convert_right_join()))
               YYABORT;
-            add_join_on($$, $9);
+            add_join_natural($$,$5,$9);
           }
 	| table_ref NATURAL RIGHT opt_outer JOIN_SYM table_factor
 	  {
             YYERROR_UNLESS($1 && $6);
-	    add_join_natural($6,$1);
+	    add_join_natural($6,$1,NULL);
 	    LEX *lex= Lex;
             if (!($$= lex->current_select->convert_right_join()))
               YYABORT;
 	  }
 	| table_ref NATURAL JOIN_SYM table_factor
-	  { YYERROR_UNLESS($1 && ($$=$4)); add_join_natural($1,$4); };
+	  { YYERROR_UNLESS($1 && ($$=$4)); add_join_natural($1,$4,NULL); };
 
 
 normal_join:
@@ -5235,8 +5283,23 @@ table_factor:
 	    YYABORT;
           sel->add_joined_table($$);
 	}
-	| '{' ident table_ref LEFT OUTER JOIN_SYM table_ref ON expr '}'
-	  { YYERROR_UNLESS($3 && $7); add_join_on($7,$9); $7->outer_join|=JOIN_TYPE_LEFT; $$=$7; }
+	| '{' ident table_ref LEFT OUTER JOIN_SYM table_ref
+          ON
+          {
+            /* Change the current name resolution context to a local context. */
+            Name_resolution_context *on_context;
+            if (!(on_context= make_join_on_context(YYTHD,$3,$7)))
+              YYABORT;
+            Lex->push_context(on_context);
+          }
+          expr '}'
+	  {
+            YYERROR_UNLESS($3 && $7);
+            add_join_on($7,$10);
+            Lex->pop_context();
+            $7->outer_join|=JOIN_TYPE_LEFT;
+            $$=$7;
+          }
 	| select_derived_init get_select_lex select_derived2
           {
             LEX *lex= Lex;
@@ -5290,6 +5353,7 @@ table_factor:
 
 	      YYABORT;
             sel->add_joined_table($$);
+            lex->pop_context();
           }
 	  else
           if ($4 || $6)
@@ -5429,32 +5493,18 @@ key_usage_list2:
 using_list:
 	ident
 	  {
-	    SELECT_LEX *sel= Select;
-	    if (!($$= new Item_func_eq(new Item_field(&sel->context,
-                                                      sel->db1, sel->table1,
-						      $1.str),
-				       new Item_field(&sel->context,
-                                                      sel->db2, sel->table2,
-						      $1.str))))
+            if (!($$= new List<String>))
 	      YYABORT;
+            $$->push_back(new (YYTHD->mem_root)
+                              String((const char *) $1.str, $1.length,
+                                      system_charset_info));
 	  }
 	| using_list ',' ident
 	  {
-	    SELECT_LEX *sel= Select;
-	    if (!($$=
-                  new Item_cond_and(new
-                                    Item_func_eq(new
-                                                 Item_field(&sel->context,
-                                                            sel->db1,
-                                                            sel->table1,
-                                                            $3.str),
-                                                 new
-                                                 Item_field(&sel->context,
-                                                            sel->db2,
-                                                            sel->table2,
-                                                            $3.str)),
-                                    $1)))
-	      YYABORT;
+            $1->push_back(new (YYTHD->mem_root)
+                              String((const char *) $3.str, $3.length,
+                                      system_charset_info));
+            $$= $1;
 	  };
 
 interval:
@@ -6095,7 +6145,7 @@ values:
 
 expr_or_default:
 	expr	  { $$= $1;}
-	| DEFAULT {$$= new Item_default_value(&Select->context); }
+	| DEFAULT {$$= new Item_default_value(Lex->current_context()); }
 	;
 
 opt_insert_update:
@@ -7051,13 +7101,13 @@ table_wild:
 	ident '.' '*'
 	{
           SELECT_LEX *sel= Select;
-	  $$ = new Item_field(&sel->context, NullS, $1.str, "*");
+	  $$ = new Item_field(Lex->current_context(), NullS, $1.str, "*");
 	  sel->with_wild++;
 	}
 	| ident '.' ident '.' '*'
 	{
           SELECT_LEX *sel= Select;
-	  $$ = new Item_field(&sel->context, (YYTHD->client_capabilities &
+	  $$ = new Item_field(Lex->current_context(), (YYTHD->client_capabilities &
                              CLIENT_NO_SCHEMA ? NullS : $1.str),
                              $3.str,"*");
 	  sel->with_wild++;
@@ -7085,8 +7135,8 @@ simple_ident:
 	    SELECT_LEX *sel=Select;
 	    $$= (sel->parsing_place != IN_HAVING ||
 	         sel->get_in_sum_expr() > 0) ?
-                 (Item*) new Item_field(&sel->context, NullS, NullS, $1.str) :
-	         (Item*) new Item_ref(&sel->context, NullS, NullS, $1.str);
+                 (Item*) new Item_field(Lex->current_context(), NullS, NullS, $1.str) :
+	         (Item*) new Item_ref(Lex->current_context(), NullS, NullS, $1.str);
 	  }
         }
         | simple_ident_q { $$= $1; }
@@ -7098,8 +7148,8 @@ simple_ident_nospvar:
 	  SELECT_LEX *sel=Select;
 	  $$= (sel->parsing_place != IN_HAVING ||
 	       sel->get_in_sum_expr() > 0) ?
-              (Item*) new Item_field(&sel->context, NullS, NullS, $1.str) :
-	      (Item*) new Item_ref(&sel->context, NullS, NullS, $1.str);
+              (Item*) new Item_field(Lex->current_context(), NullS, NullS, $1.str) :
+	      (Item*) new Item_ref(Lex->current_context(), NullS, NullS, $1.str);
 	}
 	| simple_ident_q { $$= $1; }
 	;
@@ -7136,7 +7186,7 @@ simple_ident_q:
               YYABORT;
             }
 
-            if (!(trg_fld= new Item_trigger_field(&lex->current_select->context,
+            if (!(trg_fld= new Item_trigger_field(Lex->current_context(),
                                                   new_row ?
                                                   Item_trigger_field::NEW_ROW:
                                                   Item_trigger_field::OLD_ROW,
@@ -7162,8 +7212,8 @@ simple_ident_q:
 	    }
 	    $$= (sel->parsing_place != IN_HAVING ||
 	         sel->get_in_sum_expr() > 0) ?
-	        (Item*) new Item_field(&sel->context, NullS, $1.str, $3.str) :
-	        (Item*) new Item_ref(&sel->context, NullS, $1.str, $3.str);
+	        (Item*) new Item_field(Lex->current_context(), NullS, $1.str, $3.str) :
+	        (Item*) new Item_ref(Lex->current_context(), NullS, $1.str, $3.str);
           }
         }
 	| '.' ident '.' ident
@@ -7178,8 +7228,8 @@ simple_ident_q:
 	  }
 	  $$= (sel->parsing_place != IN_HAVING ||
 	       sel->get_in_sum_expr() > 0) ?
-	      (Item*) new Item_field(&sel->context, NullS, $2.str, $4.str) :
-              (Item*) new Item_ref(&sel->context, NullS, $2.str, $4.str);
+	      (Item*) new Item_field(Lex->current_context(), NullS, $2.str, $4.str) :
+              (Item*) new Item_ref(Lex->current_context(), NullS, $2.str, $4.str);
 	}
 	| ident '.' ident '.' ident
 	{
@@ -7193,11 +7243,11 @@ simple_ident_q:
 	  }
 	  $$= (sel->parsing_place != IN_HAVING ||
 	       sel->get_in_sum_expr() > 0) ?
-	      (Item*) new Item_field(&sel->context,
+	      (Item*) new Item_field(Lex->current_context(),
                                      (YYTHD->client_capabilities &
 				      CLIENT_NO_SCHEMA ? NullS : $1.str),
 				     $3.str, $5.str) :
-	      (Item*) new Item_ref(&sel->context,
+	      (Item*) new Item_ref(Lex->current_context(),
                                    (YYTHD->client_capabilities &
 				    CLIENT_NO_SCHEMA ? NullS : $1.str),
                                    $3.str, $5.str);
@@ -7761,8 +7811,7 @@ sys_option_value:
               it= new Item_null();
             }
 
-            if (!(trg_fld= new Item_trigger_field(&lex->current_select->
-                                                  context,
+            if (!(trg_fld= new Item_trigger_field(Lex->current_context(),
                                                   Item_trigger_field::NEW_ROW,
                                                   $2.base_name.str)) ||
                 !(i= new sp_instr_set_trigger_field(lex->sphead->
@@ -8618,7 +8667,12 @@ union_list:
             lex->current_select->master_unit()->union_distinct=
                                                       lex->current_select;
 	}
-	select_init {}
+	select_init
+        {
+          /* Remove from the name resolution context stack the context of the
+             last select in the union. */
+          Lex->pop_context();
+        }
 	;
 
 union_opt:
@@ -8722,6 +8776,7 @@ subselect_end:
 	')'
 	{
 	  LEX *lex=Lex;
+          lex->pop_context();
 	  lex->current_select = lex->current_select->return_after_parsing();
 	};