Test case for bug lp:1001117, MySQL BUG#12330344

Analysis:
The problem in the original MySQL bug is that the range optimizer
performs its analysis in a separate MEM_ROOT object that is freed
after the range optimzier is done. During range analysis get_mm_tree
calls Item_func_like::select_optimize, which in turn evaluates its
right argument. In the test case the right argument is a subquery.

In MySQL, subqueries are optimized lazyly, thus the call to val_str
triggers optimization for the subquery. All objects needed by the
subquery plan end up in the temporary MEM_ROOT used by the range
optimizer. When execution ends, the JOIN::cleanup process tries to
cleanup objects of the subquery plan, but all these objects are gone
with the temporary MEM_ROOT. The solution for MySQL is to switch the
mem_root.

In MariaDB with the patch for bug lp:944706, all constant subqueries
that may be used by the optimization process are preoptimized. Therefore
Item_func_like::select_optimize only triggers subquery execution, and
the above problem is not present.

The patch however adds a test whether the evaluated right argument of
the LIKE predicate is expensive. This is consistent with our approach
not to evaluate expensive expressions during optimization.

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index b45b138ced2..560373b69e6 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -4736,7 +4736,7 @@ longlong Item_func_like::val_int()
 
 Item_func::optimize_type Item_func_like::select_optimize() const
 {
-  if (args[1]->const_item())
+  if (args[1]->const_item() && !args[1]->is_expensive())
   {
     String* res2= args[1]->val_str((String *)&cmp.value2);
     const char *ptr2;