>Description:
MAX fails to return the correct value in some MERGE table situations.
Based on experimentation I am guessing that the query fails to read all
of the member tables when the query can be performed entirely by reading
the index.
I seem to be able to reproduce this every time on MySQL 3.23.51, .55, and
one of the versions in between (but I forget which). I don't believe this
is the same as any of the known bugs listed in "MERGE table problems" in
the docs. But I could be wrong.
>How-To-Repeat:
Here is a sequence of commands that can be source-d:
-- optional
drop table if exists whole;
drop table if exists part1;
drop table if exists part2;
-- create tables
create table part1 (id int(10) not null, value int(10), key (id, value));
create table part2 (id int(10) not null, value int(10), key (id, value));
create table whole (id int(10) not null, value int(10), key (id, value))
type=merge union=(part1,part2);
-- insert some values
insert into part1 values (1, 100), (2, 200), (3, 300);
insert into part2 values (1, 200), (5, 500);
-- this correctly shows all 5 rows
select * from whole;
-- this correctly shows the 2 values where id = 1
select value from whole where id = 1;
-- this ought to say 200 but says 100 instead
select max(value) from whole where id = 1;
-- this also ought to say 200 but says 100 instead
select floor(max(value)) from whole where id = 1;
-- this correctly says 200
select max(floor(value)) from whole where id = 1;
-- this also correctly says 200
select id, max(value) from whole where id = 1 group by id;
>Fix:
Workaround: in the query, replace MAX(expr) with MAX(FUNC(expr)) where
FUNC is a no-op. The original problem arose with a datetime column (I
changed it to an int for the test case above), so e.g.
FROM_UNIXTIME(MAX(UNIX_TIMESTAMP(tstamp))) works around the bug.
>Submitter-Id:
>Originator: S. Spencer Sun
>Organization:
>MySQL support: none
>Synopsis: MAX fails to return the correct value in some MERGE table situations
>Severity: serious
>Priority: high
>Category: mysql
>Class: sw-bug
>Release: mysql-3.23.55 (Source distribution)
>Server: /usr/local/bin/mysqladmin Ver 8.23 Distrib 3.23.55, for pc-linux on i686
Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL license
Server version 3.23.55-log
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /tmp/mysql.sock
Uptime: 10 min 22 sec
Threads: 1 Questions: 121 Slow queries: 0 Opens: 35 Flush tables: 1 Open tables:
6 Queries per second avg: 0.195
>Environment:
System: Linux pratt 2.2.22-6.2.2smp #2 SMP Tue Oct 22 20:32:19 PDT 2002 i686 unknown
Architecture: i686
Some paths: /usr/local/bin/perl /usr/bin/make /usr/bin/gmake /usr/bin/gcc /usr/bin/cc
GCC: Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/egcs-2.91.66/specs
gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
Compilation info: CC='gcc' CFLAGS='-O3 -mpentiumpro' CXX='gcc' CXXFLAGS='-O3
-mpentiumpro -felide-constructors -fno-exceptions -fno-rtti' LDFLAGS=''
LIBC:
lrwxrwxrwx 1 root root 13 Mar 13 2001 /lib/libc.so.6 -> libc-2.1.3.so
-rwxr-xr-x 1 root root 4106572 Sep 9 09:58 /lib/libc-2.1.3.so
-rw-r--r-- 1 root root 20336836 Sep 9 09:58 /usr/lib/libc.a
-rw-r--r-- 1 root root 178 Sep 9 09:58 /usr/lib/libc.so
Configure command: ./configure '--prefix=/usr/local' '--localstatedir=/var/mysql'
'--enable-assembler' '--with-mysqld-ldflags=-all-static' '--with-raid'
'--enable-local-infile' 'CFLAGS=-O3 -mpentiumpro' 'CXXFLAGS=-O3 -mpentiumpro
-felide-constructors -fno-exceptions -fno-rtti' 'CXX=gcc'
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