MDEV-240: SHOW EXPLAIN: Assertion `this->optimized == 2' failed

- Fix the bug: SHOW EXPLAIN may hit a case where a join is partially 
  optimized.
- Change JOIN::optimized to use enum instead of numeric constants

mysql-test/r/show_explain.result

 drop table if exists t0, t1, t2;
+drop view if exists v1;
 create table t0 (a int);
 insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
 create table t1 (a int);
@@ -337,4 +338,36 @@ Warnings:
 Note	1003	select `test`.`t2`.`a` AS `a` from `test`.`t2` join `test`.`t2` group by `test`.`t2`.`a`
 set debug='';
 DROP TABLE t2;
+#
+# MDEV-240: SHOW EXPLAIN: Assertion `this->optimized == 2' failed in 
+# JOIN::print_explain on query with a JOIN, TEMPTABLE view,
+#          
+CREATE TABLE t3 (a INT);
+CREATE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t3;
+INSERT INTO t3 VALUES (8);
+CREATE TABLE t2 (b INT);
+INSERT INTO t2 VALUES (4),(5),(6),(7),(8),(9);
+explain SELECT * FROM v1, t2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	<derived2>	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	
+2	DERIVED	t3	system	NULL	NULL	NULL	NULL	1	
+set @show_explain_probe_select_id=2;
+set debug='d,show_explain_probe_join_exec_end';
+SELECT * FROM v1, t2;
+show explain for $thr2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Not yet optimized
+Warnings:
+Note	1003	SELECT * FROM v1, t2
+a	b
+8	4
+8	5
+8	6
+8	7
+8	8
+8	9
+set debug='';
+DROP VIEW v1;
+DROP TABLE t2, t3;
 drop table t0,t1;

mysql-test/t/show_explain.test

@@ -5,6 +5,7 @@
 
 --disable_warnings
 drop table if exists t0, t1, t2;
+drop view if exists v1;
 --enable_warnings
 
 # 
@@ -346,6 +347,30 @@ set debug='';
 DROP TABLE t2;
 
 
+--echo #
+--echo # MDEV-240: SHOW EXPLAIN: Assertion `this->optimized == 2' failed in 
+--echo # JOIN::print_explain on query with a JOIN, TEMPTABLE view,
+--echo #          
+CREATE TABLE t3 (a INT); 
+CREATE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t3;
+INSERT INTO t3 VALUES (8);
+CREATE TABLE t2 (b INT);
+INSERT INTO t2 VALUES (4),(5),(6),(7),(8),(9);
+explain SELECT * FROM v1, t2;
+
+set @show_explain_probe_select_id=2;
+set debug='d,show_explain_probe_join_exec_end';
+send SELECT * FROM v1, t2;
+
+connection default;
+--source include/wait_condition.inc
+evalp show explain for $thr2;
+connection con1;
+reap;
+set debug='';
+DROP VIEW v1;
+DROP TABLE t2, t3;
+
 ## TODO: Test this: have several SHOW EXPLAIN requests be queued up for a
 ##       thread and served together.
 

sql/item_subselect.cc

@@ -2910,7 +2910,7 @@ int subselect_single_select_engine::exec()
   SELECT_LEX *save_select= thd->lex->current_select;
   thd->lex->current_select= select_lex;
 
-  if (!join->optimized)
+  if (join->optimized != JOIN::OPTIMIZATION_DONE)
   {
     SELECT_LEX_UNIT *unit= select_lex->master_unit();
 
@@ -4647,7 +4647,9 @@ int subselect_hash_sj_engine::exec()
   */
   thd->lex->current_select= materialize_engine->select_lex;
   /* The subquery should be optimized, and materialized only once. */
-  DBUG_ASSERT(materialize_join->optimized && !is_materialized);
+  DBUG_ASSERT(materialize_join->optimized == JOIN::OPTIMIZATION_DONE && 
+              !is_materialized);
+
   materialize_join->exec();
   if ((res= test(materialize_join->error || thd->is_fatal_error ||
                  thd->is_error())))

sql/sql_lex.cc

@@ -3750,7 +3750,7 @@ int st_select_lex::print_explain(select_result_sink *output,
                                  uint8 explain_flags)
 {
   int res;
-  if (join && join->optimized == 2)
+  if (join && join->optimized == JOIN::OPTIMIZATION_DONE)
   {
     res= join->print_explain(output, explain_flags, TRUE,
                              join->need_tmp, // need_tmp_table

sql/sql_select.cc

@@ -608,7 +608,7 @@ JOIN::prepare(Item ***rref_pointer_array,
   DBUG_ENTER("JOIN::prepare");
 
   // to prevent double initialization on EXPLAIN
-  if (optimized)
+  if (optimized != JOIN::NOT_OPTIMIZED)
     DBUG_RETURN(0);
 
   conds= conds_init;
@@ -936,7 +936,7 @@ err:
 int JOIN::optimize()
 {
   int res= optimize_inner();
-  optimized= 2;
+  optimized= JOIN::OPTIMIZATION_DONE;
   return res;
 }
 /**
@@ -960,9 +960,9 @@ JOIN::optimize_inner()
   DBUG_ENTER("JOIN::optimize");
   do_send_rows = (unit->select_limit_cnt) ? 1 : 0;
   // to prevent double initialization on EXPLAIN
-  if (optimized)
+  if (optimized != JOIN::NOT_OPTIMIZED)
     DBUG_RETURN(0);
-  optimized= 1;
+  optimized= JOIN::OPTIMIZATION_IN_PROGRESS;
   thd_proc_info(thd, "optimizing");
 
   set_allowed_join_cache_types();
@@ -1731,7 +1731,7 @@ int JOIN::init_execution()
 {
   DBUG_ENTER("JOIN::init_execution");
 
-  DBUG_ASSERT(optimized);
+  DBUG_ASSERT(optimized == JOIN::OPTIMIZATION_DONE);
   DBUG_ASSERT(!(select_options & SELECT_DESCRIBE));
   initialized= true;
 
@@ -21187,7 +21187,7 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
   DBUG_PRINT("info", ("Select 0x%lx, type %s, message %s",
 		      (ulong)join->select_lex, join->select_lex->type,
 		      message ? message : "NULL"));
-  DBUG_ASSERT(this->optimized == 2);
+  
   /* Don't log this into the slow query log */
 
   if (!on_the_fly)
@@ -21204,6 +21204,10 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
   {
     item_list.push_back(new Item_int((int32)
 				     join->select_lex->select_number));
+
+    if (on_the_fly)
+      join->select_lex->set_explain_type(on_the_fly);
+
     item_list.push_back(new Item_string(join->select_lex->type,
 					strlen(join->select_lex->type), cs));
     for (uint i=0 ; i < 7; i++)
@@ -21227,6 +21231,7 @@ int JOIN::print_explain(select_result_sink *result, uint8 explain_flags,
   else if (!join->select_lex->master_unit()->derived ||
            join->select_lex->master_unit()->derived->is_materialized_derived())
   {
+    DBUG_ASSERT(optimized == JOIN::OPTIMIZATION_DONE);
     table_map used_tables=0;
     //if (!join->select_lex->type)
     if (on_the_fly)

sql/sql_select.h

@@ -1178,7 +1178,11 @@ public:
   const char *zero_result_cause; ///< not 0 if exec must return zero result
   
   bool union_part; ///< this subselect is part of union 
-  int  optimized; ///< flag to avoid double optimization in EXPLAIN
+
+  enum join_optimization_state { NOT_OPTIMIZED=0,
+                                 OPTIMIZATION_IN_PROGRESS=1,
+                                 OPTIMIZATION_DONE=2};
+  join_optimization_state optimized; ///< flag to avoid double optimization in EXPLAIN
   bool initialized; ///< flag to avoid double init_execution calls
 
   /*
@@ -1261,7 +1265,7 @@ public:
     ref_pointer_array= items0= items1= items2= items3= 0;
     ref_pointer_array_size= 0;
     zero_result_cause= 0;
-    optimized= 0;
+    optimized= JOIN::NOT_OPTIMIZED;
     initialized= 0;
     cond_equal= 0;
     having_equal= 0;