fix for bug #12595 (Escape character has to be exactly one)

mysql-test/r/select.result:
  results for test of bug 12595
mysql-test/t/select.test:
  test for bug #12595
sql/item_cmpfunc.cc:
  check whether the size of the escape string is exactly 1 (bug #12595)

mysql-test/r/select.result

@@ -2739,3 +2739,14 @@ DROP TABLE t1,t2;
 select x'10' + 0, X'10' + 0, b'10' + 0, B'10' + 0;
 x'10' + 0	X'10' + 0	b'10' + 0	B'10' + 0
 16	16	2	2
+CREATE TABLE BUG_12595(a varchar(100));
+INSERT INTO BUG_12595 VALUES ('hakan%'), ('hakank'), ("ha%an");
+SELECT * FROM BUG_12595 WHERE a LIKE 'hakan*%' ESCAPE '*';
+a
+hakan%
+SELECT * FROM BUG_12595 WHERE a LIKE 'hakan**%' ESCAPE '**';
+ERROR HY000: Incorrect arguments to ESCAPE
+SELECT * FROM BUG_12595 WHERE a LIKE 'ha%%an' ESCAPE '%';
+a
+ha%an
+DROP TABLE BUG_12595;

mysql-test/t/select.test

@@ -2350,3 +2350,14 @@ DROP TABLE t1,t2;
 #
 
 select x'10' + 0, X'10' + 0, b'10' + 0, B'10' + 0;
+
+#
+# BUG #12595
+#
+CREATE TABLE BUG_12595(a varchar(100));
+INSERT INTO BUG_12595 VALUES ('hakan%'), ('hakank'), ("ha%an");
+SELECT * FROM BUG_12595 WHERE a LIKE 'hakan*%' ESCAPE '*';
+-- error 1210
+SELECT * FROM BUG_12595 WHERE a LIKE 'hakan**%' ESCAPE '**';
+SELECT * FROM BUG_12595 WHERE a LIKE 'ha%%an' ESCAPE '%';
+DROP TABLE BUG_12595;

sql/item_cmpfunc.cc

@@ -2792,8 +2792,14 @@ bool Item_func_like::fix_fields(THD *thd, Item **ref)
   {
     /* If we are on execution stage */
     String *escape_str= escape_item->val_str(&tmp_value1);
+    /* ESCAPE must be 1 char in length.*/
+    if (escape_str && escape_str->numchars() != 1)
+    {
+      my_error(ER_WRONG_ARGUMENTS,MYF(0),"ESCAPE");
+      return TRUE;
+    }
     escape= escape_str ? *(escape_str->ptr()) : '\\';
- 
+    
     /*
       We could also do boyer-more for non-const items, but as we would have to
       recompute the tables for each row it's not worth it.