MDEV-736 LP:1004615 - Unexpected warnings "Encountered illegal value '' when converting to DECIMAL" on a query with aggregate functions and GROUP BY

fix: don't call field->val_decimal() if the field->is_null()
because the buffer at field->ptr might not hold a valid decimal value

sql/item_sum.cc:
  do not call field->val_decimal() if the field->is_null()
storage/maria/ma_blockrec.c:
  cleanup
storage/maria/ma_rrnd.c:
  cleanup
strings/decimal.c:
  typo

mysql-test/r/group_by.result

@@ -2097,7 +2097,7 @@ NULL
 drop table t1;
 # End of 5.2 tests
 #
-#  BUG#872702: Crash in add_ref_to_table_cond() when grouping by a PK
+#  lp:872702 Crash in add_ref_to_table_cond() when grouping by a PK
 #
 CREATE TABLE t1 (a int, PRIMARY KEY (a)) ;
 INSERT INTO t1 VALUES (14),(15),(16),(17),(18),(19),(20);
@@ -2111,4 +2111,15 @@ FROM t2
 GROUP BY 1;
 a
 DROP TABLE t1, t2;
+FLUSH STATUS;
+CREATE TABLE t1 (f1 INT, f2 decimal(20,1), f3 blob);
+INSERT INTO t1 values(11,NULL,'blob'),(11,NULL,'blob');
+SELECT f3, MIN(f2) FROM t1 GROUP BY f1 LIMIT 1;
+f3	MIN(f2)
+blob	NULL
+DROP TABLE t1;
+the value below *must* be 1
+show status like 'Created_tmp_disk_tables';
+Variable_name	Value
+Created_tmp_disk_tables	1
 # End of 5.3 tests

mysql-test/t/group_by.test

@@ -1456,7 +1456,7 @@ drop table t1;
 --echo # End of 5.2 tests
 
 --echo #
---echo #  BUG#872702: Crash in add_ref_to_table_cond() when grouping by a PK
+--echo #  lp:872702 Crash in add_ref_to_table_cond() when grouping by a PK
 --echo #
 CREATE TABLE t1 (a int, PRIMARY KEY (a)) ;
 INSERT INTO t1 VALUES (14),(15),(16),(17),(18),(19),(20);
@@ -1472,4 +1472,18 @@ WHERE a = (
 GROUP BY 1;
 DROP TABLE t1, t2;
 
+#
+# MDEV-736 LP:1004615 - Unexpected warnings "Encountered illegal value '' when converting to DECIMAL" on a query with aggregate functions and GROUP BY
+#
+
+FLUSH STATUS; # this test case *must* use Aria temp tables
+
+CREATE TABLE t1 (f1 INT, f2 decimal(20,1), f3 blob);
+INSERT INTO t1 values(11,NULL,'blob'),(11,NULL,'blob');
+SELECT f3, MIN(f2) FROM t1 GROUP BY f1 LIMIT 1;
+DROP TABLE t1;
+
+--echo the value below *must* be 1
+show status like 'Created_tmp_disk_tables';
+
 --echo # End of 5.3 tests

sql/item_sum.cc

@@ -2149,9 +2149,8 @@ Item_sum_hybrid::min_max_update_int_field()
 void
 Item_sum_hybrid::min_max_update_decimal_field()
 {
-  /* TODO: optimize: do not get result_field in case of args[0] is NULL */
   my_decimal old_val, nr_val;
-  const my_decimal *old_nr= result_field->val_decimal(&old_val);
+  const my_decimal *old_nr;
   const my_decimal *nr= args[0]->val_decimal(&nr_val);
   if (!args[0]->null_value)
   {
@@ -2159,16 +2158,17 @@ Item_sum_hybrid::min_max_update_decimal_field()
       old_nr=nr;
     else
     {
+      old_nr= result_field->val_decimal(&old_val);
       bool res= my_decimal_cmp(old_nr, nr) > 0;
       /* (cmp_sign > 0 && res) || (!(cmp_sign > 0) && !res) */
       if ((cmp_sign > 0) ^ (!res))
         old_nr=nr;
     }
     result_field->set_notnull();
+    result_field->store_decimal(old_nr);
   }
   else if (result_field->is_null(0))
     result_field->set_null();
-  result_field->store_decimal(old_nr);
 }
 
 

storage/maria/ma_blockrec.c

@@ -4676,7 +4676,7 @@ int _ma_read_block_record2(MARIA_HA *info, uchar *record,
                            uchar *data, uchar *end_of_data)
 {
   MARIA_SHARE *share= info->s;
-  uchar *field_length_data, *blob_buffer, *start_of_data;
+  uchar *UNINIT_VAR(field_length_data), *UNINIT_VAR(blob_buffer), *start_of_data;
   uint flag, null_bytes, cur_null_bytes, row_extents, field_lengths;
   my_bool found_blob= 0;
   MARIA_EXTENT_CURSOR extent;
@@ -4684,9 +4684,6 @@ int _ma_read_block_record2(MARIA_HA *info, uchar *record,
   MARIA_ROW *cur_row= &info->cur_row;
   DBUG_ENTER("_ma_read_block_record2");
 
-  LINT_INIT(field_length_data);
-  LINT_INIT(blob_buffer);
-
   start_of_data= data;
   flag= (uint) (uchar) data[0];
   cur_null_bytes= share->base.original_null_bytes;
@@ -5114,6 +5111,7 @@ int _ma_read_block_record(MARIA_HA *info, uchar *record,
   uchar *data, *end_of_data, *buff;
   uint offset;
   uint block_size= share->block_size;
+  int ret;
   DBUG_ENTER("_ma_read_block_record");
   DBUG_PRINT("enter", ("rowid: %lu  page: %lu  rownr: %u",
                        (ulong) record_pos,
@@ -5135,7 +5133,8 @@ int _ma_read_block_record(MARIA_HA *info, uchar *record,
     my_errno= HA_ERR_RECORD_DELETED;           /* File crashed */
     DBUG_RETURN(HA_ERR_RECORD_DELETED);
   }
-  DBUG_RETURN(_ma_read_block_record2(info, record, data, end_of_data));
+  ret= _ma_read_block_record2(info, record, data, end_of_data);
+  DBUG_RETURN(ret);
 }
 
 

storage/maria/ma_rrnd.c

@@ -30,6 +30,7 @@
 
 int maria_rrnd(MARIA_HA *info, uchar *buf, MARIA_RECORD_POS filepos)
 {
+  int ret;
   DBUG_ENTER("maria_rrnd");
 
   DBUG_ASSERT(filepos != HA_OFFSET_ERROR);
@@ -40,5 +41,6 @@ int maria_rrnd(MARIA_HA *info, uchar *buf, MARIA_RECORD_POS filepos)
     DBUG_RETURN(my_errno);
 
   info->cur_row.lastpos= filepos;               /* Remember for update */
-  DBUG_RETURN((*info->s->read_record)(info, buf, filepos));
+  ret= (*info->s->read_record)(info, buf, filepos);
+  DBUG_RETURN(ret);
 }

strings/decimal.c

@@ -1190,7 +1190,7 @@ int decimal2longlong(const decimal_t *from, longlong *to)
 
     And for -1234567890.1234 it would be
 
-                7E F2 04 37 2D FB 2D
+                7E F2 04 C7 2D FB 2D
 */
 int decimal2bin(const decimal_t *from, uchar *to, int precision, int frac)
 {