Manually merged

mysql-test/t/select.test:
  Auto merged
sql/item_cmpfunc.cc:
  Auto merged

mysql-test/r/select.result

@@ -3389,3 +3389,9 @@ a	t1.b + 0	t1.c + 0	a	t2.b + 0	c	d
 1	0	1	1	0	1	NULL
 2	0	1	NULL	NULL	NULL	NULL
 drop table t1,t2;
+CREATE TABLE t1 (i BIGINT UNSIGNED NOT NULL);
+INSERT INTO t1 VALUES (10);
+SELECT i='1e+01',i=1e+01, i in (1e+01), i in ('1e+01') FROM t1;
+i='1e+01'	i=1e+01	i in (1e+01)	i in ('1e+01')
+0	1	1	1
+DROP TABLE t1;

mysql-test/t/select.test

@@ -2285,6 +2285,25 @@ EXPLAIN SELECT * FROM t1 FORCE INDEX (a);
 
 DROP TABLE t1;
 
+#
+# Bug #18759 "Incorrect string to numeric conversion"
+#
+# This test is here so that the behavior will not be changed to 4.1
+# and not to 5.0 either. In 4.1 and 5.0 sending an integer as a string
+# will be converted internally to real (double) value and it is not
+# as accurate as bigint (longlong) for integers. Thus the results may
+# vary. In 5.1 internally it is decimal, which is a string type and
+# will be more accurate. Due to rather big changes needed to fix this
+# in 4.1 or 5.0 it is not desired to do it in the stable versions.
+#
+# This test is here only to make sure that behavior is not changed in
+# 4.1 and 5.0
+#
+CREATE TABLE t1 (i BIGINT UNSIGNED NOT NULL);
+INSERT INTO t1 VALUES (10);
+SELECT i='1e+01',i=1e+01, i in (1e+01), i in ('1e+01') FROM t1;
+DROP TABLE t1;
+
 # End of 4.1 tests
 
 #

sql/item_cmpfunc.cc

@@ -138,7 +138,8 @@ static void agg_cmp_type(THD *thd, Item_result *type, Item **items, uint nitems)
       }
       continue;
     }
-    if ((res= items[i]->real_item()->type()) == Item::FIELD_ITEM)
+    if ((res= items[i]->real_item()->type()) == Item::FIELD_ITEM &&
+        items[i]->result_type() != INT_RESULT)
     {
       field= ((Item_field *)items[i]->real_item())->field;
       break;