Fix for bug #24558: Increasing decimal column length causes data loss

Altering to a decimal field we get double value then store it 
that may cause data loss. 
Fix: use store_decimal() instead.



mysql-test/r/type_newdecimal.result:
  Fix for bug #24558: Increasing decimal column length causes data loss
    - test result.
mysql-test/t/type_newdecimal.test:
  Fix for bug #24558: Increasing decimal column length causes data loss
    - test case.
sql/field_conv.cc:
  Fix for bug #24558: Increasing decimal column length causes data loss
    - if target field's result type is DECIMAL_RESULT
      use store_decimal(val_decimal()) in order not to loss data.

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/field_conv.cc b/sql/field_conv.cc
index dbe58d804ad..32180f0a93e 100644
--- a/sql/field_conv.cc
+++ b/sql/field_conv.cc
@@ -337,6 +337,13 @@ static void do_field_real(Copy_field *copy)
 }
 
 
+static void do_field_decimal(Copy_field *copy)
+{
+  my_decimal value;
+  copy->to_field->store_decimal(copy->from_field->val_decimal(&value));
+}
+
+
 /*
   string copy for single byte characters set when to string is shorter than
   from string
@@ -581,6 +588,8 @@ void (*Copy_field::get_copy_func(Field *to,Field *from))(Copy_field*)
     if (to->real_type() == FIELD_TYPE_BIT ||
         from->real_type() == FIELD_TYPE_BIT)
       return do_field_int;
+    if (to->result_type() == DECIMAL_RESULT)
+      return do_field_decimal;
     // Check if identical fields
     if (from->result_type() == STRING_RESULT)
     {