Fix QUOTE() to not reuse the input field for output, which resulted in

incorrect results when the input was a constant across a multi-row SELECT
statement. (Bug #8248)

mysql-test/r/func_str.result

@@ -297,3 +297,10 @@ quote(ltrim(concat('    ', 'a')))
 select quote(trim(concat('    ', 'a')));
 quote(trim(concat('    ', 'a')))
 'a'
+CREATE TABLE t1 SELECT 1 UNION SELECT 2 UNION SELECT 3;
+SELECT QUOTE('A') FROM t1;
+QUOTE('A')
+'A'
+'A'
+'A'
+DROP TABLE t1;

mysql-test/t/func_str.test

@@ -193,3 +193,8 @@ select trim(leading 'foo' from 'foo');
 
 select quote(ltrim(concat('    ', 'a')));
 select quote(trim(concat('    ', 'a')));
+
+# Bad results from QUOTE(). Bug #8248
+CREATE TABLE t1 SELECT 1 UNION SELECT 2 UNION SELECT 3;
+SELECT QUOTE('A') FROM t1;
+DROP TABLE t1;

sql/item_strfunc.cc

@@ -2183,18 +2183,13 @@ String *Item_func_quote::val_str(String *str)
   for (from= (char*) arg->ptr(), end= from + arg_length; from < end; from++)
     new_length+= get_esc_bit(escmask, (uchar) *from);
 
-  /*
-    We have to use realloc() instead of alloc() as we want to keep the
-    old result in arg
-  */
-  if (arg->realloc(new_length))
+  if (tmp_value.alloc(new_length))
     goto null;
 
   /*
-    As 'arg' and 'str' may be the same string, we must replace characters
-    from the end to the beginning
+    We replace characters from the end to the beginning
   */
-  to= (char*) arg->ptr() + new_length - 1;
+  to= (char*) tmp_value.ptr() + new_length - 1;
   *to--= '\'';
   for (start= (char*) arg->ptr(),end= start + arg_length; end-- != start; to--)
   {
@@ -2222,9 +2217,9 @@ String *Item_func_quote::val_str(String *str)
     }
   }
   *to= '\'';
-  arg->length(new_length);
+  tmp_value.length(new_length);
   null_value= 0;
-  return arg;
+  return &tmp_value;
 
 null:
   null_value= 1;

sql/item_strfunc.h

@@ -535,6 +535,7 @@ class Item_func_export_set: public Item_str_func
 
 class Item_func_quote :public Item_str_func
 {
+  String tmp_value;
 public:
   Item_func_quote(Item *a) :Item_str_func(a) {}
   const char *func_name() const { return "quote"; }