MDEV-17399: JSON_TABLE: Fix the problem with cross-nested-join dependency

Fix for for the problem with
- Cross-outer-join dependency
- dead-end join prefix
- join order pruning

See the comments in the patch for detailed description

mysql-test/suite/json/r/json_table.result

@@ -462,5 +462,34 @@ select min(x) from json_table('[]', '$' COLUMNS(x FOR ORDINALITY)) a;
 min(x)
 1
 #
-# End of 10.5 tests
+# Test for the problem with 
+#   - Cross-outer-join dependency
+#   - dead-end join prefix
+#   - join order pruning
+#
+create table t20 (a int not null);
+create table t21 (a int not null primary key, js varchar(100));
+insert into t20 select seq from seq_1_to_100;
+insert into t21 select a, '{"a":100}' from t20;
+create table t31(a int);
+create table t32(b int);
+insert into t31 values (1);
+insert into t32 values (1);
+explain
+select
+t20.a, jt1.ab
+from
+t20
+left join t21 on t20.a=t21.a
+join
+(t31 left join (t32 join JSON_TABLE(t21.js,'$' COLUMNS (ab INT PATH '$.a')) AS jt1) on t31.a<3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t31	system	NULL	NULL	NULL	NULL	1	
+1	SIMPLE	t20	ALL	NULL	NULL	NULL	NULL	100	
+1	SIMPLE	t21	eq_ref	PRIMARY	PRIMARY	4	test.t20.a	1	
+1	SIMPLE	t32	ALL	NULL	NULL	NULL	NULL	1	Using where
+1	SIMPLE	jt1	ALL	NULL	NULL	NULL	NULL	40	Table function: json_table
+drop table t20,t21,t31,t32;
+#
+# End of 10.6 tests
 #

mysql-test/suite/json/t/json_table.test

@@ -1,3 +1,5 @@
+--source include/have_sequence.inc
+
 select * from json_table('[{"a": 1, "b": [11,111]}, {"a": 2, "b": [22,222]}]', '$[*]' COLUMNS( a INT PATH '$.a')) as tt;
 
 select * from JSON_TABLE( '[ {"a": 1, "b": [11,111]}, {"a": 2, "b": [22,222]}, {"a":3}]', '$[*]' COLUMNS( a INT PATH '$.a', NESTED PATH '$.b[*]' COLUMNS (b INT PATH '$'))) as jt;
@@ -347,5 +349,34 @@ select * from json_table('[]', '$' COLUMNS(x FOR ORDINALITY));
 select min(x) from json_table('[]', '$' COLUMNS(x FOR ORDINALITY)) a;
 
 --echo #
---echo # End of 10.5 tests
+--echo # Test for the problem with 
+--echo #   - Cross-outer-join dependency
+--echo #   - dead-end join prefix
+--echo #   - join order pruning
+--echo #
+
+create table t20 (a int not null);
+create table t21 (a int not null primary key, js varchar(100));
+
+insert into t20 select seq from seq_1_to_100;
+insert into t21 select a, '{"a":100}' from t20;
+
+create table t31(a int);
+create table t32(b int);
+insert into t31 values (1);
+insert into t32 values (1);
+
+explain
+select
+  t20.a, jt1.ab
+from
+  t20
+  left join t21 on t20.a=t21.a
+  join
+  (t31 left join (t32 join JSON_TABLE(t21.js,'$' COLUMNS (ab INT PATH '$.a')) AS jt1) on t31.a<3);
+
+drop table t20,t21,t31,t32;
+
+--echo #
+--echo # End of 10.6 tests
 --echo #

sql/json_table.cc

@@ -1284,3 +1284,117 @@ void Table_function_json_table::fix_after_pullout(TABLE_LIST *sql_table,
 }
 
 
+/*
+  @brief
+     Recursively make all tables in the join_list also depend on deps.
+*/
+
+static void add_extra_deps(List<TABLE_LIST> *join_list, table_map deps)
+{
+  TABLE_LIST *table;
+  List_iterator<TABLE_LIST> li(*join_list);
+  while ((table= li++))
+  {
+    table->dep_tables |= deps;
+    NESTED_JOIN *nested_join;
+    if ((nested_join= table->nested_join))
+    {
+       // set the deps inside, too
+       add_extra_deps(&nested_join->join_list, deps);
+    }
+  }
+}
+
+
+/*
+  @brief
+    Add extra dependencies implied by table functions so that the join
+    optimizer does not construct "dead-end" join prefixes.
+
+  @detail
+    There are two kinds of limitations on join order:
+    1A. Outer joins require that inner tables follow outer.
+    1B. Tables within a join nest must be present in the join order
+        "without interleaving". See check_interleaving_with_nj for details.
+
+    2. Table function argument may refer to *any* table that precedes the
+    current table in the query text. The table maybe outside of the current
+    nested join and/or inside another nested join.
+
+    @example
+
+      select ...
+      from
+        t20 left join t21 on t20.a=t21.a
+      join
+        (t31 left join (t32 join
+                        JSON_TABLE(t21.js,
+                                   '$' COLUMNS (ab INT PATH '$.a')) AS jt
+                       ) on t31.a<3
+        )
+
+      Here, jt's argument refers to t21.
+
+      Table dependencies are:
+        t21 -> t20
+        t32 -> t31
+        jt  -> t21 t31  (also indirectly depends on t20 through t21)
+
+      This allows to construct a "dead-end" join prefix, like:
+
+       t31, t32
+
+      Here, "no interleaving" rule requires the next table to be jt, but we
+      can't add it, because it depends on t21 which is not in the join prefix.
+
+    @end example
+
+    Dead-end join prefixes do not work with join prefix pruning done for
+    @@optimizer_prune_level: it is possible that all non-dead-end prefixes are
+    pruned away.
+
+    The solution is as follows: if there is an outer join that contains
+    (directly on indirectly) a table function JT which has a reference JREF
+    outside of the outer join:
+
+      left join ( T_I ... json_table(JREF, ...) as JT ...)
+
+    then make *all* tables T_I also dependent on outside references in JREF.
+    This way, the optimizer will put table T_I into the join prefix only when
+    JT can be put there as well, and "dead-end" prefixes will not be built.
+
+  @param  join_list    List of tables to process. Initial invocation should
+                       supply the JOIN's top-level table list.
+  @param  nest_tables  Bitmap of all tables in the join list.
+
+  @return Bitmap of all outside references that tables in join_list have
+*/
+
+table_map add_table_function_dependencies(List<TABLE_LIST> *join_list,
+                                          table_map nest_tables)
+{
+  TABLE_LIST *table;
+  table_map res= 0;
+  List_iterator<TABLE_LIST> li(*join_list);
+
+  // Recursively compute extra dependencies
+  while ((table= li++))
+  {
+    NESTED_JOIN *nested_join;
+    if ((nested_join= table->nested_join))
+    {
+      res |= add_table_function_dependencies(&nested_join->join_list,
+                                             nested_join->used_tables);
+    }
+    else if (table->table_function)
+      res |= table->dep_tables;
+  }
+  res= res & ~nest_tables & ~PSEUDO_TABLE_BITS;
+  // Then, make all "peers" have them:
+  if (res)
+    add_extra_deps(join_list,  res);
+
+  return res;
+}
+
+

sql/json_table.h

@@ -252,5 +252,8 @@ private:
 
 TABLE *create_table_for_function(THD *thd, TABLE_LIST *sql_table);
 
+table_map add_table_function_dependencies(List<TABLE_LIST> *join_list,
+                                          table_map nest_tables);
+
 #endif /* JSON_TABLE_INCLUDED */
 

sql/sql_select.cc

@@ -1924,6 +1924,9 @@ JOIN::optimize_inner()
 
     /* Convert all outer joins to inner joins if possible */
     conds= simplify_joins(this, join_list, conds, TRUE, FALSE);
+
+    add_table_function_dependencies(join_list, table_map(-1));
+
     if (thd->is_error() || select_lex->save_leaf_tables(thd))
     {
       if (arena)