MDEV-37933: Rewrite [NATURAL] FULL OUTER to LEFT, RIGHT, or INNER JOIN

mysql-test/main/join.test

@@ -2073,34 +2073,34 @@ explain extended select * from t1 natural full outer join t2;
 select * from t1 natural full join t2;
 explain extended select * from t1 natural full join t2;
 
-create view v1 as select * from t1 full join t2 on t1.a = t2.a;
+create view v1 as select t1.a as t1a, t2.a as t2a from t1 full join t2 on t1.a = t2.a;
 --error ER_NOT_SUPPORTED_YET
 select * from v1;
 explain extended select * from v1;
 drop view v1;
 
-create view v1 as select * from t1 full outer join t2 on t1.a = t2.a;
+create view v1 as select t1.a as t1a, t2.a as t2a from t1 full outer join t2 on t1.a = t2.a;
 --error ER_NOT_SUPPORTED_YET
 select * from v1;
 explain extended select * from v1;
 drop view v1;
 
-create view v1 as select * from t1 natural full join t2;
+create view v1 as select t1.a as t1a, t2.a as t2a from t1 natural full join t2;
 --error ER_NOT_SUPPORTED_YET
 select * from v1;
 explain extended select * from v1;
 drop view v1;
 
-create view v1 as select * from t1 natural full outer join t2;
+create view v1 as select t1.a as t1a, t2.a as t2a from t1 natural full outer join t2;
 --error ER_NOT_SUPPORTED_YET
 select * from v1;
 explain extended select * from v1;
 drop view v1;
 
---error ER_BAD_FIELD_ERROR
+--error ER_NOT_SUPPORTED_YET
 select * from (select t1.a from t1 full join t2 on t1.a = t2.a union select * from t1) dt;
 
---error ER_BAD_FIELD_ERROR
+--error ER_NOT_SUPPORTED_YET
 select * from (select t1.a from t1 full outer join t2 on t1.a = t2.a union select * from t1) dt;
 
 --error ER_NOT_SUPPORTED_YET
@@ -2127,7 +2127,104 @@ select * from t1, t2 natural full join t3;
 --error ER_NO_SUCH_TABLE
 select * from t1, t2 natural full outer join t3;
 
+--error ER_FULL_JOIN_BASE_TABLES_ONLY
+select * from (select * from t1) dt natural full join (select * from t2) du;
+
+--error ER_FULL_JOIN_BASE_TABLES_ONLY
+select * from (select * from t1) dt natural full join t2;
+
+--error ER_FULL_JOIN_BASE_TABLES_ONLY
+select * from t1 natural full join (select * from t2) du;
+
 drop table t1, t2;
+
+--echo # Exercise FULL JOIN rewrites to LEFT, RIGHT, and INNER JOIN.
+create table x (pk int auto_increment, x int, y int, primary key (pk));
+create table xsq (pk int auto_increment, x int, y int, primary key (pk));
+insert into x (x, y) values (-5,-5),(-4,-4),(-3,-3),(-2,-2),(-1,-1),(0,0),(1,1),(2,2),(3,3),(4,4),(5,5);
+insert into xsq (x, y) values (-5,25),(-4,16),(-3,9),(-2,4),(-1,1),(0,0),(1,1),(2,4),(3,9),(4,16),(5,25);
+
+--echo # FULL to RIGHT JOIN, these two queries should be equal:
+select * from x  full join xsq on x.y = xsq.y where xsq.pk is not null;
+select * from x right join xsq on x.y = xsq.y;
+
+--echo # FULL to RIGHT JOIN, these two queries should be equal:
+select * from x  full join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1 where xsq.pk is not null;
+select * from x right join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1;
+
+--echo # FULL to INNER JOIN, these two queries should be equal:
+select * from x  full join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1 where x.pk is not null and xsq.pk is not null;
+select * from x inner join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1;
+
+--echo # FULL to LEFT JOIN, these two queries should be equal:
+select * from x full join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1 where x.pk is not null;
+select * from x left join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1;
+
+--echo # FULL NATURAL to INNER JOIN, these two queries should be equal:
+select * from x natural full join xsq where x.pk is not null and xsq.pk is not null;
+select * from x inner join xsq on x.x = xsq.x and x.y = xsq.y;
+
+--echo # FULL NATURAL to LEFT JOIN, these two queries should be equal:
+select * from x natural full join xsq where x.pk is not null;
+select * from x left join xsq on xsq.pk = x.pk and xsq.x = x.x and xsq.y = x.y;
+
+--echo # FULL NATURAL to RIGHT JOIN
+select * from x natural full join xsq where xsq.pk is not null;
+select * from x right join xsq on x.pk = xsq.pk and x.x = xsq.x and x.y = xsq.y;
+
+--echo # These two will fail because it cannot be rewritten to a LEFT, RIGHT, nor INNER JOIN.
+--error ER_NOT_SUPPORTED_YET
+select * from x full join xsq on x.x >= 0 and x.x <= 1 and xsq.x >= 0 and xsq.x <= 1;
+--error ER_NOT_SUPPORTED_YET
+select * from x natural full join xsq;
+
+drop table x, xsq;
+
+--echo # Nested JOINs
+create table one (v int);
+insert into one (v) values (1);
+create table two (v int);
+insert into two (v) values (2);
+create table three (v int);
+insert into three (v) values (3);
+
+--echo # (FULL)FULL to (INNER)INNER JOIN
+select * from one full join two on one.v = two.v full join three on two.v = three.v where one.v is not null and two.v is not null and three.v is not null;
+select * from one inner join two on one.v = two.v inner join three on two.v = three.v;
+
+--echo # (FULL)FULL to (RIGHT)LEFT JOIN
+select * from one full join two on one.v = two.v full join three on one.v = three.v where two.v is not null;
+select * from one right join two on one.v = two.v left join three on one.v = three.v;
+
+--echo # (FULL)FULL to (LEFT)LEFT JOIN
+select * from one full join two on one.v = two.v full join three on one.v = three.v where one.v is not null;
+select * from one left join two on two.v = one.v left join three on three.v = one.v;
+
+--echo # (FULL)LEFT to (LEFT)LEFT JOIN
+select * from one full join two on one.v = two.v left join three on two.v = three.v where one.v is not null;
+select * from one left join two on one.v = two.v left join three on two.v = three.v;
+
+--echo # (FULL)LEFT to (RIGHT)LEFT JOIN
+select * from one full join two on one.v = two.v left join three on two.v = three.v where two.v is not null;
+select * from one right join two on one.v = two.v left join three on three.v = two.v;
+
+--echo # (LEFT)FULL to (LEFT)RIGHT JOIN
+select * from one left join two on one.v = two.v full join three on two.v = three.v where three.v is not null;
+select * from one left join two on one.v = two.v right join three on two.v = three.v;
+
+--echo # (LEFT)FULL to (LEFT)LEFT JOIN
+insert into one (v) values (2),(3);
+insert into two (v) values (1);
+truncate three;
+insert into three (v) values (1);
+select * from one;
+select * from two;
+select * from three;
+select * from one left join two on one.v = two.v full join three on two.v = three.v where three.v = 1;
+select * from three left join one on one.v = 1 left join two on two.v = 1;
+
+drop table one, two, three;
+
 # TODO fix PS protocol before end of FULL OUTER JOIN development
 --enable_ps_protocol
 --echo # End of 12.3 tests

sql/share/errmsg-utf8.txt

@@ -12362,3 +12362,5 @@ ER_WARN_CONFLICTING_COMPOUND_INDEX_HINT_FOR_KEY
         eng "Hint %s is ignored as conflicting/duplicated (an index hint of the same type or opposite kind has already been specified for the key)"
 ER_WARN_NO_IMPLICIT_QB_NAMES_IN_VIEW
 	eng "Implicit query block names are ignored for hints specified within VIEWs"
+ER_FULL_JOIN_BASE_TABLES_ONLY
+        eng "FULL JOIN supported for base tables only, %s is not a base table"

sql/sql_base.cc

@@ -7998,6 +7998,23 @@ store_top_level_join_columns(THD *thd, TABLE_LIST *table_ref,
 }
 
 
+/*
+  If the tables involved participate in a FULL OUTER JOIN then don't
+  update their name resolution contexts at this point, or it will
+  break simplify_joins.
+ */
+static bool is_full_outer_join(Name_resolution_context *context,
+                               TABLE_LIST *right_neighbor)
+{
+  const uint ctx_outer_join= context->first_name_resolution_table->outer_join;
+  const uint rtn_outer_join=
+    right_neighbor->first_leaf_for_name_resolution()->outer_join;
+
+  return (ctx_outer_join & JOIN_TYPE_FULL) ||
+         (rtn_outer_join & JOIN_TYPE_FULL);
+}
+
+
 /*
   Compute and store the row types of the top-most NATURAL/USING joins
   in a FROM clause.
@@ -8085,8 +8102,9 @@ static bool setup_natural_join_row_types(THD *thd,
     FROM clause.
   */
   DBUG_ASSERT(right_neighbor);
-  context->first_name_resolution_table=
-    right_neighbor->first_leaf_for_name_resolution();
+  if (!is_full_outer_join(context, right_neighbor))
+    context->first_name_resolution_table=
+      right_neighbor->first_leaf_for_name_resolution();
   /*
     This is only to ensure that first_name_resolution_table doesn't
     change on re-execution

sql/sql_list.h

@@ -597,6 +597,34 @@ template <class T> class List_iterator :public base_list_iterator
   inline void remove()      { base_list_iterator::remove(); }
   inline void after(T *a)   { base_list_iterator::after(a); }
   inline T** ref(void)	    { return (T**) base_list_iterator::ref(); }
+
+  /*
+    Swap the current element with the next one in the list.
+
+    If this iterator points to no element or to the last element, then this
+    method does nothing and returns nullptr.
+
+    If this iter points to B in the following list
+      A, B, C, D, ...
+    then after this method returns, the list will be
+      A, C, B, D, ...
+    and this method returns C.  This iter will point to the same location
+    in the list after this method returns as it did before, but the element at
+    that location will be C instead of B.
+
+    Other iterators pointing to the same list remain valid and will see the
+    updated list order.
+  */
+  T* swap_next()
+  {
+    if (!ref() || !*ref() || !peek())
+      return nullptr;
+    T* cur= *ref();
+    List_iterator<T> itr= *this;
+    T* nxt= itr++;
+    replace(nxt);
+    return itr.replace(cur);
+  }
 };
 
 

sql/sql_parse.cc

@@ -8672,12 +8672,10 @@ bool st_select_lex::add_cross_joined_table(TABLE_LIST *left_op,
 
 TABLE_LIST *st_select_lex::convert_right_join()
 {
-  TABLE_LIST *tab2= join_list->pop();
-  TABLE_LIST *tab1= join_list->pop();
   DBUG_ENTER("convert_right_join");
-
-  join_list->push_front(tab2, parent_lex->thd->mem_root);
-  join_list->push_front(tab1, parent_lex->thd->mem_root);
+  List_iterator<TABLE_LIST> li(*join_list);
+  li++; // points iterator at first element and returns it
+  TABLE_LIST* tab1= li.swap_next();
   tab1->outer_join|= JOIN_TYPE_RIGHT;
 
   DBUG_RETURN(tab1);