opt_sum.cc:

  A fix for a bug #3189, pertaining to crashing MySQL server when a query with MIN / MAX on the BLOB column is to be optimised

mysql-test/r/type_blob.result

@@ -601,3 +601,9 @@ id	txt
 2	Chevy 
 4	Ford
 drop table t1;
+CREATE TABLE t1 ( i int(11) NOT NULL default '0',    c text NOT NULL, PRIMARY KEY  (i), KEY (c(1),c(1)));
+INSERT t1 VALUES (1,''),(2,''),(3,'asdfh'),(4,'');
+select max(i) from t1 where c = '';
+max(i)
+4
+drop table t1;

mysql-test/t/type_blob.test

@@ -312,3 +312,9 @@ select * from t1 where txt <= 'Chevy';
 select * from t1 where txt > 'Chevy';
 select * from t1 where txt >= 'Chevy';
 drop table t1;
+CREATE TABLE t1 ( i int(11) NOT NULL default '0',    c text NOT NULL, PRIMARY KEY  (i), KEY (c(1),c(1)));
+INSERT t1 VALUES (1,''),(2,''),(3,'asdfh'),(4,'');
+select max(i) from t1 where c = '';
+drop table t1;
+
+

sql/opt_sum.cc

@@ -443,7 +443,9 @@ static bool find_range_key(TABLE_REF *ref, Field* field, COND *cond)
 	// Save found constant
 	if (part->null_bit)
 	  *key_ptr++= (byte) test(part->field->is_null());
-	part->field->get_key_image((char*) key_ptr,part->length);
+	part->field->get_key_image((char*) key_ptr,
+				   (part->field->type() == FIELD_TYPE_BLOB) ? 
+				   part->length + HA_KEY_BLOB_LENGTH : part->length);
 	key_ptr+=part->store_length - test(part->null_bit);
 	left_length-=part->store_length;
       }