Bug#47669 Query showed by EXPLAIN EXTENDED gives different result from original query

Item_field::print method does not take into
account fields whose values may be null.
The fix is to print 'NULL' if field value is null.


mysql-test/r/explain.result:
  test case
mysql-test/r/func_str.result:
  result fix
mysql-test/r/having.result:
  result fix
mysql-test/r/select.result:
  result fix
mysql-test/r/subselect.result:
  result fix
mysql-test/r/union.result:
  result fix
mysql-test/t/explain.test:
  test case
sql/item.cc:
  print 'NULL' if field value is null.

1 files changed, 8 insertions, 3 deletions

diff --git a/sql/item.cc b/sql/item.cc
index 934e897f923..04496338b8f 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -5690,9 +5690,14 @@ void Item_field::print(String *str, enum_query_type query_type)
     char buff[MAX_FIELD_WIDTH];
     String tmp(buff,sizeof(buff),str->charset());
     field->val_str(&tmp);
-    str->append('\'');
-    str->append(tmp);
-    str->append('\'');
+    if (field->is_null())
+      str->append("NULL");
+    else
+    {
+      str->append('\'');
+      str->append(tmp);
+      str->append('\'');
+    }
     return;
   }
   Item_ident::print(str, query_type);