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.

Author: igorbabaev

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

@@ -665,25 +665,29 @@ 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)
  {
  next_sl= sl->next_select(); 
  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())
  {
  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;