MDEV-7827: Assertion `!table || (!table->read_set ||...

MDEV-7827: Assertion `!table || (!table->read_set || bitmap_is_set(table->read_set, field_index))' failed in Field_long::val_str on EXPLAIN EXTENDED

(Solution by Sergei Petrunia)
It appeared that semijoin conditions was not iterated when we were updating used tables. So now they do.

mysql-test/r/derived.result

@@ -580,3 +580,28 @@ select x.id, message from (select id from t1) x left join
 where coalesce(message,0) <> 0;
 id	message
 drop table t1,t2;
+#
+# MDEV-7827: Assertion `!table || (!table->read_set ||
+# bitmap_is_set(table->read_set, field_index))' failed
+# in Field_long::val_str on EXPLAIN EXTENDED
+#
+CREATE TABLE t1 (f1 INT, f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (6,9);
+CREATE TABLE t2 (f3 INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (2),(0);
+EXPLAIN EXTENDED
+SELECT f1 FROM ( SELECT * FROM t1 ) AS sq
+WHERE f1 IN (
+SELECT f3 FROM t2 WHERE f2 IN (
+SELECT f3 FROM t2 HAVING f3 >= 8
+)
+);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	PRIMARY	<subquery4>	eq_ref	distinct_key	distinct_key	4	test.t1.f2	1	100.00	
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; FirstMatch(<subquery4>); Using join buffer (flat, BNL join)
+4	MATERIALIZED	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	
+Warnings:
+Note	1276	Field or reference 'f2' of SELECT #3 was resolved in SELECT #1
+Note	1003	select 6 AS `f1` from  <materialize> (select `test`.`t2`.`f3` from `test`.`t2` having (`test`.`t2`.`f3` >= 8)) semi join (`test`.`t2`) where ((`test`.`t2`.`f3` = 6) and (9 = `<subquery4>`.`f3`))
+DROP TABLE t2,t1;

mysql-test/t/derived.test

@@ -506,3 +506,25 @@ select x.id, message from (select id from t1) x left join
 (select id, 1 as message from t2) y on x.id=y.id
 where coalesce(message,0) <> 0;
 drop table t1,t2;
+
+--echo #
+--echo # MDEV-7827: Assertion `!table || (!table->read_set ||
+--echo # bitmap_is_set(table->read_set, field_index))' failed
+--echo # in Field_long::val_str on EXPLAIN EXTENDED
+--echo #
+
+CREATE TABLE t1 (f1 INT, f2 INT, KEY(f2)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (6,9);
+
+CREATE TABLE t2 (f3 INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (2),(0);
+
+EXPLAIN EXTENDED
+SELECT f1 FROM ( SELECT * FROM t1 ) AS sq
+WHERE f1 IN (
+  SELECT f3 FROM t2 WHERE f2 IN (
+    SELECT f3 FROM t2 HAVING f3 >= 8
+  )
+);
+
+DROP TABLE t2,t1;

sql/sql_lex.cc

@@ -3866,6 +3866,19 @@ void SELECT_LEX::update_used_tables()
       tl->on_expr->update_used_tables();
       tl->on_expr->walk(&Item::eval_not_null_tables, 0, NULL);
     }
+    /*
+      - There is no need to check sj_on_expr, because merged semi-joins inject
+        sj_on_expr into the parent's WHERE clase.
+      - For non-merged semi-joins (aka JTBMs), we need to check their
+        left_expr. There is no need to check the rest of the subselect, we know
+        it is uncorrelated and so cannot refer to any tables in this select.
+    */
+    if (tl->jtbm_subselect)
+    {
+      Item *left_expr= tl->jtbm_subselect->left_expr;
+      left_expr->walk(&Item::update_table_bitmaps_processor, FALSE, NULL);
+    }
+
     embedding= tl->embedding;
     while (embedding)
     {