MDEV-15581 Incorrect result (missing row) with UNION DISTINCT in anchor parts

The current code does not support recursive CTEs whose specifications
contain a mix of ALL UNION and DISTINCT UNION operations.
This patch catches such specifications and reports errors for them.

mysql-test/r/cte_recursive.result

@@ -3243,3 +3243,23 @@ SELECT 1 FROM qn
 ORDER BY (SELECT * FROM qn))
 SELECT count(*) FROM qn;
 ERROR 42000: This version of MariaDB doesn't yet support 'global ORDER_BY/LIMIT in recursive CTE spec'
+#
+# MDEV-15581: mix of ALL and DISTINCT UNION in recursive CTE
+#
+create table t1(a int);
+insert into t1 values(1),(2);
+insert into t1 values(1),(2);
+set @c=0, @d=0;
+WITH RECURSIVE qn AS
+(
+select 1,0 as col from t1
+union distinct
+select 1,0 from t1
+union all
+select 3, 0*(@c:=@c+1) from qn where @c<1
+union all
+select 3, 0*(@d:=@d+1) from qn where @d<1
+)
+select * from qn;
+ERROR 42000: This version of MariaDB doesn't yet support 'mix of ALL and DISTINCT UNION operations in recursive CTE spec'
+drop table t1;

mysql-test/t/cte_recursive.test

@@ -2258,3 +2258,27 @@ SELECT 1 FROM dual UNION ALL
 SELECT 1 FROM qn
 ORDER BY (SELECT * FROM qn))
 SELECT count(*) FROM qn;
+
+--echo #
+--echo # MDEV-15581: mix of ALL and DISTINCT UNION in recursive CTE
+--echo #
+
+create table t1(a int);
+insert into t1 values(1),(2);
+insert into t1 values(1),(2);
+
+set @c=0, @d=0;
+--error ER_NOT_SUPPORTED_YET
+WITH RECURSIVE qn AS
+(
+select 1,0 as col from t1
+union distinct
+select 1,0 from t1
+union all
+select 3, 0*(@c:=@c+1) from qn where @c<1
+union all
+select 3, 0*(@d:=@d+1) from qn where @d<1
+)
+select * from qn;
+
+drop table t1;

sql/sql_cte.cc

@@ -665,7 +665,6 @@ void With_element::move_anchors_ahead()
 {
   st_select_lex *next_sl;
   st_select_lex *new_pos= spec->first_select();
-  st_select_lex *UNINIT_VAR(last_sl);
   new_pos->linkage= UNION_TYPE;
   for (st_select_lex *sl= new_pos; sl; sl= next_sl)
   {
@@ -673,6 +672,14 @@ void With_element::move_anchors_ahead()
     if (is_anchor(sl))
     {
       sl->move_node(new_pos);
+      if (new_pos == spec->first_select())
+      {
+        enum sub_select_type type= new_pos->linkage;
+        new_pos->linkage= sl->linkage;
+        sl->linkage= type;
+        new_pos->with_all_modifier= sl->with_all_modifier;
+        sl->with_all_modifier= false;
+      }
       new_pos= sl->next_select();
     }
     else if (!sq_rec_ref && no_rec_ref_on_top_level())
@@ -680,10 +687,7 @@ void With_element::move_anchors_ahead()
       sq_rec_ref= find_first_sq_rec_ref_in_select(sl);
       DBUG_ASSERT(sq_rec_ref != NULL);
     }
-    last_sl= sl;
   }
-  if (spec->union_distinct)
-    spec->union_distinct= last_sl;
   first_recursive= new_pos;
 }
 

sql/sql_lex.cc

@@ -2171,6 +2171,7 @@ void st_select_lex::init_select()
   select_limit= 0;      /* denotes the default limit = HA_POS_ERROR */
   offset_limit= 0;      /* denotes the default offset = 0 */
   with_sum_func= 0;
+  with_all_modifier= 0;
   is_correlated= 0;
   cur_pos_in_select_list= UNDEF_POS;
   cond_value= having_value= Item::COND_UNDEF;

sql/sql_lex.h

@@ -907,6 +907,7 @@ class st_select_lex: public st_select_lex_node
   */
   bool subquery_in_having;
   /* TRUE <=> this SELECT is correlated w.r.t. some ancestor select */
+  bool with_all_modifier;  /* used for selects in union */
   bool is_correlated;
   /*
     This variable is required to ensure proper work of subqueries and

sql/sql_union.cc

@@ -453,6 +453,23 @@ bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
   DBUG_ASSERT(thd == thd_arg);
   DBUG_ASSERT(thd == current_thd);
 
+  if (is_recursive && (sl= first_sl->next_select()))
+  {
+    SELECT_LEX *next_sl;
+    for ( ; ; sl= next_sl)
+    {
+      next_sl= sl->next_select();
+      if (!next_sl)
+        break;
+      if (next_sl->with_all_modifier != sl->with_all_modifier)
+      {
+        my_error(ER_NOT_SUPPORTED_YET, MYF(0),
+         "mix of ALL and DISTINCT UNION operations in recursive CTE spec");
+        DBUG_RETURN(TRUE);
+      }
+    }
+  }
+
   describe= additional_options & SELECT_DESCRIBE;
 
   /*

sql/sql_yacc.yy

@@ -707,6 +707,7 @@ bool add_select_to_union_list(LEX *lex, bool is_union_distinct,
     return TRUE;
   mysql_init_select(lex);
   lex->current_select->linkage=UNION_TYPE;
+  lex->current_select->with_all_modifier= !is_union_distinct;
   if (is_union_distinct) /* UNION DISTINCT - remember position */
     lex->current_select->master_unit()->union_distinct=
       lex->current_select;