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, 1 insertions, 0 deletions

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index d3ddd9e208c..3624b238fbc 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -671,6 +671,7 @@ void lex_start(THD *thd)
   lex->curr_with_clause= 0;
   lex->with_clauses_list= 0;
   lex->with_clauses_list_last_next= &lex->with_clauses_list;
+  lex->clone_spec_offset= 0;
   lex->value_list.empty();
   lex->update_list.empty();
   lex->set_var_list.empty();