A fix (bug #6564: QUOTE(NULL) returns NULL, not the string 'NULL')

mysql-test/r/func_str.result

@@ -167,6 +167,9 @@ length(quote(concat(char(0),"test")))
 select hex(quote(concat(char(224),char(227),char(230),char(231),char(232),char(234),char(235))));
 hex(quote(concat(char(224),char(227),char(230),char(231),char(232),char(234),char(235))))
 27E0E3E6E7E8EAEB27
+select concat('a', quote(NULL));
+concat('a', quote(NULL))
+aNULL
 select reverse("");
 reverse("")
 
@@ -278,7 +281,7 @@ insert into t1 values ('one'),(NULL),('two'),('four');
 select a, quote(a), isnull(quote(a)), quote(a) is null, ifnull(quote(a), 'n') from t1;
 a	quote(a)	isnull(quote(a))	quote(a) is null	ifnull(quote(a), 'n')
 one	'one'	0	0	'one'
-NULL	NULL	1	1	n
+NULL	NULL	0	0	NULL
 two	'two'	0	0	'two'
 four	'four'	0	0	'four'
 drop table t1;

mysql-test/t/func_str.test

@@ -69,6 +69,12 @@ select quote(1/0), quote('\0\Z');
 select length(quote(concat(char(0),"test")));
 select hex(quote(concat(char(224),char(227),char(230),char(231),char(232),char(234),char(235))));
 
+#
+# Bug #6564: QUOTE(NULL
+#
+
+select concat('a', quote(NULL));
+
 #
 # Wrong usage of functions
 #

sql/item_strfunc.cc

@@ -2142,9 +2142,12 @@ String* Item_func_inet_ntoa::val_str(String* str)
 
     This function is very useful when you want to generate SQL statements
 
-    RETURN VALUES
+  NOTE
+    QUOTE(NULL) returns the string 'NULL' (4 letters, without quotes).
+
+  RETURN VALUES
     str		Quoted string
-    NULL	Argument to QUOTE() was NULL or out of memory.
+    NULL	Out of memory.
 */
 
 #define get_esc_bit(mask, num) (1 & (*((mask) + ((num) >> 3))) >> ((num) & 7))
@@ -2168,7 +2171,12 @@ String *Item_func_quote::val_str(String *str)
   String *arg= args[0]->val_str(str);
   uint arg_length, new_length;
   if (!arg)					// Null argument
-    goto null;
+  {
+    str->copy("NULL", 4);			// Return the string 'NULL'
+    null_value= 0;
+    return str;
+  }
+
   arg_length= arg->length();
   new_length= arg_length+2; /* for beginning and ending ' signs */