Fixed bug #28980: the result of ROUND(<decimal expr>,<int column>)

was erroneously converted to double, while the result of
ROUND(<decimal expr>, <int literal>) was preserved as decimal.
As a result of such a conversion the value of ROUND(D,A) could
differ from the value of ROUND(D,val(A)) if D was a decimal expression.

Now the result of the ROUND function is never converted to 
double if the first argument is decimal.  


mysql-test/r/type_decimal.result:
  Added a test case for bug #28980.
mysql-test/t/type_decimal.test:
  Added a test case for bug #28980.

1 files changed, 7 insertions, 1 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index cc8830c6d6f..ab4a9c50332 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -1957,7 +1957,13 @@ void Item_func_round::fix_length_and_dec()
   {
     max_length= args[0]->max_length;
     decimals= args[0]->decimals;
-    hybrid_type= REAL_RESULT;
+    if (args[0]->result_type() == DECIMAL_RESULT)
+    {
+      max_length++;
+      hybrid_type= DECIMAL_RESULT;
+    }
+    else
+      hybrid_type= REAL_RESULT;
     return;
   }