What I often do:

my $sql="$a where ";
my @where;
push @where, $b if $b;
push @where, $c if $c;

$sql .= join " and ", @where;

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Usually the push'es are in a block where the variables are being created, so I don't need the 'if $b' or 'if $c' clauses.
This also lets me create an @args array so that I can use placeholders in the where clauses and use the array of arguments during the execute (assuming that you're using DBI). Eg:
my $sql="$a where ";
my (@where, @args);

if ($something) {
 push @where, "field1 = ?";
 push @args, $some_value; 
}
if ($something_else) {
 push @where, "field2 = ?";
 push @args, $another_value;
}
$sql .= join " and ", @where;
# Assume RaiseError is true;
# If this is executed more than once
# in this script,
# use 'prepare_cached' instead.
my $sth = $dbh->prepare($sql);
$sth->execute(@args);

[download]
Some of the many benefits of placeholders are that you don't have to escape quotes (or generally any other character), you can prepare the statement once and execute it many times with different arguments, and even if you DO only execute it once in this script, some databases can cache the statement and so using placeholders can let the database utilize the cache more efficiently over multiple executions with different arguments.

In reply to Re: 3 strings to join by runrig
in thread 3 strings to join by jptxs

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