MDEV-5581: Server crashes in in JOIN::prepare on 2nd execution of PS with materialization+semijoin

- The problem was that JOIN::prepare() tried to set TABLE::maybe_null
  for a table in join. Non-merged semi-join tables 1) are present as 
  join's base tables on second EXECUTE, but 2) do not yet have a TABLE 
  object.
  Worked around the problem by putting mixed_implicit_grouping into JOIN
  object, and then passing it to JTBM tables in setup_jtbm_semi_joins().

mysql-test/r/subselect_sj.result

@@ -2782,4 +2782,20 @@ db
 mysql
 information_schema
 DROP TABLE t1;
+#
+# MDEV-5581: Server crashes in in JOIN::prepare on 2nd execution of PS with materialization+semijoin
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (2),(3);
+CREATE TABLE t2 (b INT);
+INSERT INTO t2 VALUES (8),(9);
+CREATE TABLE t3 (c INT, INDEX(c));
+INSERT INTO t2 VALUES (5),(6);
+PREPARE stmt FROM 
+"SELECT * FROM t1 WHERE ( 9, 5 ) IN ( SELECT b, COUNT(*) FROM t2 WHERE 1 IN ( SELECT MIN(c) FROM t3 ) )";
+EXECUTE stmt;
+a
+EXECUTE stmt;
+a
+DROP TABLE t1,t2,t3;
 set optimizer_switch=@subselect_sj_tmp;

mysql-test/r/subselect_sj_jcl6.result

@@ -2796,6 +2796,22 @@ db
 information_schema
 mysql
 DROP TABLE t1;
+#
+# MDEV-5581: Server crashes in in JOIN::prepare on 2nd execution of PS with materialization+semijoin
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (2),(3);
+CREATE TABLE t2 (b INT);
+INSERT INTO t2 VALUES (8),(9);
+CREATE TABLE t3 (c INT, INDEX(c));
+INSERT INTO t2 VALUES (5),(6);
+PREPARE stmt FROM 
+"SELECT * FROM t1 WHERE ( 9, 5 ) IN ( SELECT b, COUNT(*) FROM t2 WHERE 1 IN ( SELECT MIN(c) FROM t3 ) )";
+EXECUTE stmt;
+a
+EXECUTE stmt;
+a
+DROP TABLE t1,t2,t3;
 set optimizer_switch=@subselect_sj_tmp;
 #
 # BUG#49129: Wrong result with IN-subquery with join_cache_level=6 and firstmatch=off

mysql-test/t/subselect_sj.test

@@ -2489,5 +2489,24 @@ INSERT INTO t1 VALUES ('mysql'),('information_schema');
 SELECT * FROM t1 WHERE db IN (SELECT `SCHEMA_NAME` FROM information_schema.SCHEMATA); 
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-5581: Server crashes in in JOIN::prepare on 2nd execution of PS with materialization+semijoin
+--echo #
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (2),(3);
+
+CREATE TABLE t2 (b INT);
+INSERT INTO t2 VALUES (8),(9);
+
+CREATE TABLE t3 (c INT, INDEX(c));
+INSERT INTO t2 VALUES (5),(6);
+
+PREPARE stmt FROM 
+"SELECT * FROM t1 WHERE ( 9, 5 ) IN ( SELECT b, COUNT(*) FROM t2 WHERE 1 IN ( SELECT MIN(c) FROM t3 ) )";
+EXECUTE stmt;
+EXECUTE stmt;
+
+DROP TABLE t1,t2,t3;
+
 # The following command must be the last one the file 
 set optimizer_switch=@subselect_sj_tmp;

sql/opt_subselect.cc

@@ -5204,6 +5204,7 @@ bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,
         if (!(*join_where)->fixed)
           (*join_where)->fix_fields(join->thd, join_where);
       }
+      table->table->maybe_null= test(join->mixed_implicit_grouping);
     }
 
     if ((nested_join= table->nested_join))

sql/sql_select.cc

@@ -616,7 +616,7 @@ JOIN::prepare(Item ***rref_pointer_array,
     aggregate functions in the SELECT list is a MySQL exptenstion that
     is allowed only if the ONLY_FULL_GROUP_BY sql mode is not set.
   */
-  bool mixed_implicit_grouping= false;
+  mixed_implicit_grouping= false;
   if ((~thd->variables.sql_mode & MODE_ONLY_FULL_GROUP_BY) &&
       select_lex->with_sum_func && !group_list)
   {
@@ -655,7 +655,7 @@ JOIN::prepare(Item ***rref_pointer_array,
       Note: this loop doesn't touch tables inside merged semi-joins, because
       subquery-to-semijoin conversion has not been done yet. This is intended.
     */
-    if (mixed_implicit_grouping)
+    if (mixed_implicit_grouping && tbl->table)
       tbl->table->maybe_null= 1;
   }
 

sql/sql_select.h

@@ -1111,6 +1111,7 @@ public:
   JOIN *tmp_join;
   ROLLUP rollup;				///< Used with rollup
   
+  bool mixed_implicit_grouping;
   bool select_distinct;				///< Set if SELECT DISTINCT
   /**
     If we have the GROUP BY statement in the query,