Fix LP BUG#680038

Analysis:
Single-row subqueries are not considered expensive and are
evaluated both during EXPLAIN in to detect errors like
"Subquery returns more than 1 row", and during optimization to
perform constant optimization.

The cause for the failed ASSERT is in JOIN::join_free, where we set
  bool full= (!select_lex->uncacheable && !thd->lex->describe);
Thus for EXPLAIN statements full == FALSE, and as a result the call to
JOIN::cleanup doesn't call JOIN_TAB::cleanup which should have
called table->disable_keyread().

Solution:
Consider all kinds of subquery predicates as expensive.

1 files changed, 26 insertions, 0 deletions

diff --git a/mysql-test/t/subselect4.test b/mysql-test/t/subselect4.test
index 286fd321afe..786a20d6b30 100644
--- a/mysql-test/t/subselect4.test
+++ b/mysql-test/t/subselect4.test
@@ -451,6 +451,32 @@ GROUP BY t1.f4 ORDER BY t1.f1 LIMIT 10;
 drop table t1, t2, t3;
 
 --echo #
+--echo # LP BUG#680038 bool close_thread_table(THD*, TABLE**):
+--echo #               Assertion `table->key_read == 0' failed in EXPLAIN
+--echo #
+
+CREATE TABLE t1 (f1 int,f3 int,f4 int) ;
+INSERT IGNORE INTO t1 VALUES (NULL,1,0);
+
+CREATE TABLE t2 (f2 int,f4 int,f5 int) ;
+INSERT IGNORE INTO t2 VALUES (8,0,0),(5,0,0);
+
+CREATE TABLE t3 (f4 int,KEY (f4)) ;
+INSERT IGNORE INTO t3 VALUES (0),(0);
+
+set @@optimizer_switch='semijoin=off';
+
+EXPLAIN
+SELECT * FROM t1 WHERE
+(SELECT f2 FROM t2
+ WHERE f4 <= ALL
+       (SELECT SQ1_t1.f4
+        FROM t3 AS SQ1_t1 JOIN t3 AS SQ1_t3 ON SQ1_t3.f4
+        GROUP BY SQ1_t1.f4));
+
+drop table t1, t2, t3;
+
+--echo #
 --echo # BUG#52317: Assertion failing in Field_varstring::store() 
 --echo # 	    at field.cc:6833
 --echo #