>Description:
It seems that IF() is not evaluating ISNULL() well
when ISNULL() is evaluating an indexed and left-joined column,
and the returning expression is returned by COUNT().
>How-To-Repeat:
1. When tr.pcode is not indexed:
mysql> SELECT tp.pcode, IF(ISNULL(tr.pcode), 0, COUNT(*)) AS count
FROM tp
LEFT JOIN tr ON tp.pcode = tr.pcode
GROUP BY tp.pcode;
+---------+-------+
| pcode | count |
+---------+-------+
| kvw2000 | 28 |
| kvw2001 | 0 |
+---------+-------+ (as expected)
2. When tr.pcode is indexed:
mysql> SELECT tp.pcode, IF(ISNULL(tr.pcode), 0, COUNT(*)) AS count
FROM tp
LEFT JOIN tr ON tp.pcode = tr.pcode
GROUP BY tp.pcode;
+---------+-------+
| pcode | count |
+---------+-------+
| kvw2000 | 28 |
| kvw2001 | 1 |
+---------+-------+ (not as expected)
3. When tr.pcode is indexed, but COUNT() is not used:
mysql> SELECT tp.pcode, IF(ISNULL(tr.pcode), 0, 1) AS count
FROM tp
LEFT JOIN tr ON tp.pcode = tr.pcode
GROUP BY tp.pcode;
+---------+-------+
| pcode | count |
+---------+-------+
| kvw2000 | 1 |
| kvw2001 | 0 |
+---------+-------+ (as expected)
>Fix:
>Submitter-Id: <submitter ID>
>Originator:
>Organization:
>MySQL support: [none | licence | email support | extended email support ]
>Synopsis: IF(), ISNULL(), and COUNT() problem
>Severity:
>Priority:
>Category: mysql
>Class:
>Release: mysql-3.22.25 (Source distribution)
>Server: /usr/local/bin/mysqladmin Ver 7.11 Distrib 3.22.25, for pc-linux-gnu on i686
TCX Datakonsult AB, by Monty
Server version 3.22.25
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /tmp/mysql.sock
Uptime: 29 days 11 hours 16 min 33 sec
Threads: 8 Questions: 31041 Slow queries: 0 Opens: 49 Flush tables: 1 Open tables: 18
>Environment:
System: Linux kepler.snu.ac.kr 2.2.5-15 #1 Mon Apr 19 23:00:46 EDT 1999 i686 unknown
Architecture: i686
Some paths: /usr/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='' CXX='c++' CXXFLAGS='' LDFLAGS=''
Configure command: ./configure --with-charset=euc_kr --localstatedir=/home/data
Perl: This is perl, version 5.005_03 built for i386-linux
