MySQL Bugs: #1188: GROUP_CONCAT crashes on a sub-query that returns 0 rows

Bug #1188	GROUP_CONCAT crashes on a sub-query that returns 0 rows
Submitted:	3 Sep 2003 9:29	Modified:	4 Sep 2003 5:05
Reporter:	Oliver Tupman	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server	Severity:	S2 (Serious)
Version:	4.1.0-alpha-max-nt	OS:	Windows (Windows 2000)
Assigned to:	Bugs System	CPU Architecture:	Any

Description:
Query that fails is this:

SELECT GROUP_CONCAT(BugID  SEPARATOR  ",") as knownIssueIDs
FROM (
  SELECT *
  FROM BugComment
  GROUP BY BugComment.BugID
) as t1

If the sub-query returns 1 or more rows then it's fine (returns a comma seperated list). 

If sub-query returns 0 rows then MySQL crashes. Not sure how to elicit a stack-trace. Will provide if someone can tell me how.

How to repeat:
Try GROUP_CONCAT on a sub-query that will return 0 rows.

Verified.

Program received signal SIGSEGV, Segmentation fault.
0x80cde80 in copy_fields (param=0xab92948) at sql_select.cc:7980
7980        (*ptr->do_copy)(ptr);
(gdb) bt
#0  0x80cde80 in copy_fields (param=0xab92948) at sql_select.cc:7980
#1  0x8059a76 in Item_func_group_concat::add (this=0xab91170)
    at item_sum.cc:1703
#2  0x82d0fe2 in Item_sum::no_rows_in_result (this=0xab91170) at item_sum.h:65
#3  0x80c4aaa in return_zero_rows (join=0xac04028, result=0xab928f8,
    tables=0xab91768, fields=@0xab7f3c4, send_row=true, select_options=0,
    info=0x833b4a0 "no matching row in const table", having=0x0,
    procedure=0x0, unit=0xab7f29c) at sql_select.cc:3877
#4  0x80bdb5e in JOIN::exec (this=0xac04028) at sql_select.cc:1082
#5  0x80bf239 in mysql_select (thd=0xab7f018, rref_pointer_array=0xab7f45c,
    tables=0xab91768, wild_num=0, fields=@0xab7f3c4, conds=0x0, og_num=0,
    order=0x0, group=0x0, having=0x0, proc_param=0x0, select_options=17339392,
    result=0xab928f8, unit=0xab7f29c, select_lex=0xab7f364,
    tables_and_fields_initied=false) at sql_select.cc:1538
#6  0x80bb8b7 in handle_select (thd=0xab7f018, lex=0xab7f290, result=0xab928f8)
    at sql_select.cc:188
#7  0x809ced8 in mysql_execute_command (thd=0xab7f018) at sql_parse.cc:1769
#8  0x80a1c4d in mysql_parse (thd=0xab7f018,
    inBuf=0xab91028 "SELECT GROUP_CONCAT(BugID  SEPARATOR  \",\") as knownIssueIDs\nFROM 
(\n  SELECT *\n  FROM BugComment\n  GROUP BY BugComment.BugID\n) as t1", length=131) at 
sql_parse.cc:3681
#9  0x809bc87 in dispatch_command (command=COM_QUERY, thd=0xab7f018,
    packet=0xabcf019 "", packet_length=132) at sql_parse.cc:1285
#10 0x809b637 in do_command (thd=0xab7f018) at sql_parse.cc:1120
#11 0x809acec in handle_one_connection (arg=0xab7f018) at sql_parse.cc:899
#12 0x2850741f in _thread_start () from /usr/lib/libc_r.so.4
#13 0x0 in ?? ()

This has been fixed in our BK tree and the fix will be available in 4.1.1.