Merge moonbone.local:/mnt/gentoo64/work/15757-bug-5.0-opt-mysql

into  moonbone.local:/mnt/gentoo64/work/25373-bug-5.0-opt-mysql

mysql-test/r/func_str.result

@@ -1940,6 +1940,17 @@ abcxx
 select lpad('abc', cast(5 as unsigned integer), 'x');
 lpad('abc', cast(5 as unsigned integer), 'x')
 xxabc
+create table t1(f1 longtext);
+insert into t1 values ("123"),("456");
+select substring(f1,1,1) from t1 group by 1;
+substring(f1,1,1)
+1
+4
+create table t2(f1 varchar(3));
+insert into t1 values ("123"),("456");
+select substring(f1,4,1), substring(f1,-4,1) from t2;
+substring(f1,4,1)	substring(f1,-4,1)
+drop table t1,t2;
 DROP TABLE IF EXISTS t1;
 CREATE TABLE `t1` (
 `id` varchar(20) NOT NULL,

mysql-test/t/func_str.test

@@ -1008,6 +1008,17 @@ select repeat('a', cast(2 as unsigned int));
 select rpad('abc', cast(5 as unsigned integer), 'x');
 select lpad('abc', cast(5 as unsigned integer), 'x');
 
+#
+# Bug#15757: Wrong SUBSTRING() result when a tmp table was employed.
+#
+create table t1(f1 longtext);
+insert into t1 values ("123"),("456");
+select substring(f1,1,1) from t1 group by 1;
+create table t2(f1 varchar(3));
+insert into t1 values ("123"),("456");
+select substring(f1,4,1), substring(f1,-4,1) from t2;
+drop table t1,t2;
+
 #
 # Bug #25197 :repeat function returns null when using table field directly as count
 #

sql/item_strfunc.cc

@@ -1184,11 +1184,10 @@ void Item_func_substr::fix_length_and_dec()
   if (args[1]->const_item())
   {
     int32 start= (int32) args[1]->val_int();
-    start= (int32)((start < 0) ? max_length + start : start - 1);
-    if (start < 0 || start >= (int32) max_length)
-      max_length=0; /* purecov: inspected */
+    if (start < 0)
+      max_length= ((uint)(-start) > max_length) ? 0 : (uint)(-start);
     else
-      max_length-= (uint) start;
+      max_length-= min((uint)(start - 1), max_length);
   }
   if (arg_count == 3 && args[2]->const_item())
   {