Merge olga.mysql.com:/home/igor/mysql-5.0-opt

into  olga.mysql.com:/home/igor/dev-opt/mysql-5.0-opt-bug27130

mysql-test/r/func_str.result

@@ -2137,4 +2137,19 @@ id
 3
 4
 DROP TABLE t1;
+SELECT SUBSTR('foo',1,0) FROM DUAL;
+SUBSTR('foo',1,0)
+
+SELECT SUBSTR('foo',1,CAST(0 AS SIGNED)) FROM DUAL;
+SUBSTR('foo',1,CAST(0 AS SIGNED))
+
+SELECT SUBSTR('foo',1,CAST(0 AS UNSIGNED)) FROM DUAL;
+SUBSTR('foo',1,CAST(0 AS UNSIGNED))
+
+CREATE TABLE t1 (a varchar(10), len int unsigned);
+INSERT INTO t1 VALUES ('bar', 2), ('foo', 0);
+SELECT SUBSTR(a,1,len) FROM t1;
+SUBSTR(a,1,len)
+ba
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/func_str.test

@@ -1109,4 +1109,19 @@ SELECT id FROM t1 WHERE LOCATE(a,p) <=> NULL;
 
 DROP TABLE t1;
 
+#
+# Bug #27130: SUBSTR with UNSIGNED 0 as the last argument
+#
+
+SELECT SUBSTR('foo',1,0) FROM DUAL;
+SELECT SUBSTR('foo',1,CAST(0 AS SIGNED)) FROM DUAL;
+SELECT SUBSTR('foo',1,CAST(0 AS UNSIGNED)) FROM DUAL;
+
+CREATE TABLE t1 (a varchar(10), len int unsigned);
+INSERT INTO t1 VALUES ('bar', 2), ('foo', 0);
+
+SELECT SUBSTR(a,1,len) FROM t1;
+
+DROP TABLE t1; 
+
 --echo End of 5.0 tests

sql/item_strfunc.cc

@@ -1145,8 +1145,9 @@ String *Item_func_substr::val_str(String *str)
 		   (arg_count == 3 && args[2]->null_value))))
     return 0; /* purecov: inspected */
 
-  /* Negative length, will return empty string. */
-  if ((arg_count == 3) && (length <= 0) && !args[2]->unsigned_flag)
+  /* Negative or zero length, will return empty string. */
+  if ((arg_count == 3) && (length <= 0) && 
+      (length == 0 || !args[2]->unsigned_flag))
     return &my_empty_string;
 
   /* Assumes that the maximum length of a String is < INT_MAX32. */