MDEV-17154 Multiple selects from parametrized CTE fails with syntax error

This patch fills a serious flaw in the implementation of common table
expressions. Before this patch an attempt to prepare a statement from
a query with a parameter marker in a CTE that was used more than once
in the query ended up with a bogus error message. Similarly if a statement
in a stored procedure contained a CTE whose specification used a
local variables and this CTE was referred to more than once in the
statement then the server failed to execute the stored procedure returning
a bogus error message on a non-existing field.

The problems appeared due to incorrect handling of parameter markers /
local variables in CTEs that were referred more than once.

This patch fixes the problems by differentiating between the original
occurrences of a parameter marker / local variable used in the
specification of a CTE and the corresponding occurrences used
in copies of this specification. These copies are substituted
instead of non-first references to the CTE.

The idea of the fix and even some code were taken from the MySQL
implementation of the common table expressions.

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/item.h b/sql/item.h
index 8fad8dadf22..1a280e3091f 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -28,6 +28,7 @@
 #include "field.h"                              /* Derivation */
 #include "sql_type.h"
 #include "sql_time.h"
+#include "mem_root_array.h"
 
 C_MODE_START
 #include <ma_dyncol.h>
@@ -3067,6 +3068,10 @@ public:
   bool check_vcol_func_processor(void *int_arg) {return FALSE;}
   Item *get_copy(THD *thd, MEM_ROOT *mem_root) { return 0; }
 
+  bool add_as_clone(THD *thd);
+  void sync_clones();
+  bool register_clone(Item_param *i) { return m_clones.push_back(i); }
+
 private:
   void invalid_default_param() const;
 
@@ -3082,6 +3087,12 @@ public:
 private:
   Send_field *m_out_param_info;
   bool m_is_settable_routine_parameter;
+  /*
+    Array of all references of this parameter marker used in a CTE to its clones
+    created for copies of this marker used the CTE's copies. It's used to
+    synchronize the actual value of the parameter with the values of the clones.
+  */
+  Mem_root_array<Item_param *, true> m_clones;
 };