Multi-line MySQL in Perl - mysql

Question

I am trying to pass a command to my database (MariaDB/MySQLi) but Perl's DBI is giving me an error, whatever I try. The thing is that I can execute the MySQL fine in phpMyAdmin without fault. The error that I receive is:
DBD::mysql::st execute failed: You have an error in your SQL syntax;
check the manual that corresponds to your MariaDB server version for
the right syntax to use near SELECT DISTINCT t.bf FROM wrpec t JOIN wrpec r ON t.path LIKE r.path || '%' at line 2 at
retrieve-includes.pl line 20.
DBD::mysql::st fetchrow_array failed:
fetch() without execute() at retrieve-includes.pl line 22.
The full test file (fake database obviously) is as below.
#!/usr/bin/perl
use strict;
use warnings;
use DBI;
use Data::Dumper;
my $dsn = "DBI:mysql:database=mydatabase;host=machine";
my $dbh = DBI->connect($dsn, 'root', '') or die "Couldn't connect to database: " . DBI->errstr;;
my $request_includes = "
SET sql_mode = PIPES_AS_CONCAT;
SELECT DISTINCT t.bf
FROM `wrpec` t
JOIN `wrpec` r
ON t.path LIKE r.path || '%'
WHERE r.bf = 'WRPECsmain\%hd' AND t.has_tree;";
my $sth = $dbh->prepare($request_includes) or die "Couldn't prepare statement: " . $dbh->errstr;
$sth->execute();
while (my #row = $sth->fetchrow_array()) {
print Dumper(\#row);
}
$sth->finish();
I have also tried some ideas I found online: using a clean-up sub that replaces all white-space characters by hard spaces to make sure you're passing a string, and I also tried this notation (I forgot the name) but it doesn't work either (same error).
my $request_includes = <<"REQUEST_INCLUDES";
SET sql_mode = PIPES_AS_CONCAT;
SELECT DISTINCT t.bf
FROM `wrpec` t
JOIN `wrpec` r
ON t.path LIKE r.path || '%'
WHERE r.bf = 'WRPECsmain\%hd' AND t.has_tree;
REQUEST_INCLUDES

Answer 1

You're getting a SQL syntax error because by default, DBD::mysql doesn't allow you to execute multiple statements at once. You should run two separate DBI commands instead:
$dbh->do( q{SET sql_mode = 'PIPES_AS_CONCAT'} );
my $sth = $dbh->prepare(q{
SELECT DISTINCT t.bf
FROM `wrpec` t
JOIN `wrpec` r
ON t.path LIKE r.path || '%'
WHERE r.bf = 'WRPECsmain\%hd' AND t.has_tree
});
I was trying to create a script that works on MySQL as wel as PostgreSQL without changes.
Enable MySQL's ANSI mode and double quote your identifiers:
$dbh->do( q{SET sql_mode = 'ANSI'} ) if $mysql;
my $sth = $dbh->prepare(q{
SELECT DISTINCT t.bf
FROM "wrpec" t
JOIN "wrpec" r
ON t.path LIKE r.path || '%'
WHERE r.bf = 'WRPECsmain\%hd' AND t.has_tree
});
There are a couple other issues, though:
unescaped _ and % in r.path will be interpreted as wildcards
'foo' LIKE 'foo%' is true
To only fetch rows where the t.path is a prefix of r.path, but they're not equal, do:
SELECT DISTINCT t.bf
FROM "wrpec" t
JOIN "wrpec" r
ON POSITION(t.path IN r.path) = 1
AND t.path != r.path
WHERE r.bf = 'WRPECsmain\%hd'
AND t.has_tree