Bug #18080: INSERT ... SELECT ... JOIN results in ambiguous field list error

There was an incomplete reset of the name resolution context, that caused 
INSERT ... SELECT ... JOIN statements to resolve not by joint row type calculated
for the join.
Removed the redundant re-initialization of the context, because 
mysql_insert_select_prepare() now correctly saves/restores the context.

mysql-test/r/insert_select.result

@@ -686,3 +686,8 @@ ERROR 42S22: Unknown column 'z' in 'field list'
 insert into t1(x,y) select x,z from t2 on duplicate key update x=values(t2.x);
 ERROR 42S22: Unknown column 't2.x' in 'field list'
 drop table t1,t2;
+CREATE TABLE t1 (x int, y int);
+CREATE TABLE t2 (z int, y int);
+CREATE TABLE t3 (a int, b int);
+INSERT INTO t3 (SELECT x, y FROM t1 JOIN t2 USING (y) WHERE z = 1);
+DROP TABLE IF EXISTS t1,t2,t3;

mysql-test/t/insert_select.test

@@ -225,3 +225,12 @@ insert into t1(x,y) select x,z from t2 on duplicate key update x=values(t2.x);
 drop table t1,t2; 
 
 # End of 4.1 tests
+
+#
+# Bug #18080: INSERT ... SELECT ... JOIN results in ambiguous field list error
+#
+CREATE TABLE t1 (x int, y int);
+CREATE TABLE t2 (z int, y int);
+CREATE TABLE t3 (a int, b int);
+INSERT INTO t3 (SELECT x, y FROM t1 JOIN t2 USING (y) WHERE z = 1);
+DROP TABLE IF EXISTS t1,t2,t3;

sql/sql_parse.cc

@@ -3333,15 +3333,6 @@ mysql_execute_command(THD *thd)
                                              &lex->value_list,
                                              lex->duplicates, lex->ignore)))
       {
-        /*
-          Skip first table, which is the table we are inserting in.
-          Below we set context.table_list again because the call above to
-          mysql_insert_select_prepare() calls resolve_in_table_list_only(),
-          which in turn resets context.table_list and
-          context.first_name_resolution_table.
-        */
-        select_lex->context.table_list= 
-          select_lex->context.first_name_resolution_table= second_table;
 	res= handle_select(thd, lex, result, OPTION_SETUP_TABLES_DONE);
         /*
           Invalidate the table in the query cache if something changed