Bug#21448719: WRONG RESULT FOR JSON VALUE IN OUTER JOIN WITH VIEW

Item_direct_view_ref overrides all the val_*() functions in order to
ensure that they return NULL for the null-extended values of the inner
table of an outer join. It does not override val_json(), so JSON
values could in some cases come out as not NULL when NULL is expected.

This patch provides an override for val_json() in
Item_direct_view_ref, so that JSON gets the same handling of NULL as
the other data types.

Author: kahatlen

mysql-test/r/json.result

@@ -12855,3 +12855,19 @@ null
 null
 null
 DROP TABLE t;
+#
+# Bug#21448719: WRONG RESULT FOR JSON VALUE IN OUTER JOIN WITH VIEW
+#
+CREATE TABLE t1(j1 JSON);
+CREATE TABLE t2(j2 JSON);
+CREATE VIEW v AS SELECT CAST('1' AS JSON) AS jv, j2 FROM t2;
+INSERT INTO t1 VALUES ('1');
+SELECT j1, jv, j2, JSON_ARRAY(j1, jv, j2) FROM t1 LEFT JOIN v ON j1 = jv;
+j1	jv	j2	JSON_ARRAY(j1, jv, j2)
+1	NULL	NULL	[1, null, null]
+INSERT INTO t2 VALUES ('1');
+SELECT j1, jv, j2, JSON_ARRAY(j1, jv, j2) FROM t1 LEFT JOIN v ON j1 = jv;
+j1	jv	j2	JSON_ARRAY(j1, jv, j2)
+1	1	1	[1, 1, 1]
+DROP TABLE t1, t2;
+DROP VIEW v;

mysql-test/t/json.test

@@ -5783,6 +5783,19 @@ REPLACE INTO t SELECT j FROM t;
 SELECT * FROM t;
 DROP TABLE t;
 
+--echo #
+--echo # Bug#21448719: WRONG RESULT FOR JSON VALUE IN OUTER JOIN WITH VIEW
+--echo #
+CREATE TABLE t1(j1 JSON);
+CREATE TABLE t2(j2 JSON);
+CREATE VIEW v AS SELECT CAST('1' AS JSON) AS jv, j2 FROM t2;
+INSERT INTO t1 VALUES ('1');
+SELECT j1, jv, j2, JSON_ARRAY(j1, jv, j2) FROM t1 LEFT JOIN v ON j1 = jv;
+INSERT INTO t2 VALUES ('1');
+SELECT j1, jv, j2, JSON_ARRAY(j1, jv, j2) FROM t1 LEFT JOIN v ON j1 = jv;
+DROP TABLE t1, t2;
+DROP VIEW v;
+
 # Local Variables:
 # mode: sql
 # sql-product: mysql

sql/item.cc

@@ -8772,6 +8772,17 @@ bool Item_direct_view_ref::val_bool()
 }
 
 
+bool Item_direct_view_ref::val_json(Json_wrapper *wr)
+{
+  if (has_null_row())
+  {
+    null_value= TRUE;
+    return false;
+  }
+  return super::val_json(wr);
+}
+
+
 bool Item_direct_view_ref::is_null()
 {
   if (has_null_row())

sql/item.h

@@ -4150,6 +4150,7 @@ class Item_direct_view_ref :public Item_direct_ref
   virtual my_decimal *val_decimal(my_decimal *dec);
   virtual String *val_str(String *str);
   virtual bool val_bool();
+  virtual bool val_json(Json_wrapper *wr);
   virtual bool is_null();
   virtual bool send(Protocol *prot, String *tmp);
   virtual type_conversion_status save_in_field(Field *field,