Bug #46791: Assertion failed:(table->key_read==0),function unknown

  function,file sql_base.cc

When uncacheable queries are written to a temp table the optimizer must 
preserve the original JOIN structure, because it is re-using the JOIN 
structure to read from the resulting temporary table.
This was done only for uncacheable sub-queries. 
But top level queries can also benefit from this mechanism, specially if 
they're using index access and need a reset.
Fixed by not limiting the saving of JOIN structure to subqueries
exclusively.
Added a new test file to extend the existing (large) subquery.test.

1 files changed, 30 insertions, 0 deletions

diff --git a/mysql-test/r/subselect4.result b/mysql-test/r/subselect4.result
new file mode 100644
index 00000000000..68577cb2a4c
--- /dev/null
+++ b/mysql-test/r/subselect4.result
@@ -0,0 +1,30 @@
+#
+# Bug #46791: Assertion failed:(table->key_read==0),function unknown
+#    function,file sql_base.cc
+#
+CREATE TABLE t1 (a INT, b INT, KEY(a));
+INSERT INTO t1 VALUES (1,1),(2,2);
+CREATE TABLE t2 LIKE t1;
+INSERT INTO t2 VALUES (1,1),(2,2);
+CREATE TABLE t3 LIKE t1;
+# should have 1 impossible where and 2 dependent subqueries
+EXPLAIN
+SELECT 1 FROM t1
+WHERE NOT EXISTS (SELECT 1 FROM t2 WHERE 1 = (SELECT MIN(t2.b) FROM t3))
+ORDER BY count(*);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	a	5	NULL	2	Using index; Using temporary
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
+3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
+# should not crash the next statement
+SELECT 1 FROM t1
+WHERE NOT EXISTS (SELECT 1 FROM t2 WHERE 1 = (SELECT MIN(t2.b) FROM t3))
+ORDER BY count(*);
+1
+1
+# should not crash: the crash is caused by the previous statement
+SELECT 1;
+1
+1
+DROP TABLE t1,t2,t3;
+End of 5.0 tests.