I've looked a lots of ways to generate sql dynamically. I happen to like SQL::Interp quite a bit. You simply give it a list consisting of SQL and data structure references, and it generates SQL.

Pure SQL, I find very readable. Now, the problem with pure SQL is that it is not as easy to manipulate as a data structure.

So, the question is how to make sql manipulatable? Here's one approach: put any particular thing you might want to edit on a line by itself. In my case, all of my queries were the same except for the data range I was selecting.

The SQL::Interp data structure for today's data looks like this:

sub callbacks_for_today {

    my $username = shift or confess 'must supply username';

    ["
SELECT
  *
FROM
  call_schedule
  INNER JOIN person ON (user_people_id=people.id)
WHERE
  DATE_FORMAT( `callback_time` , '%Y-%m-%d' ) = DATE_FORMAT( NOW( ) , 
+'%Y-%m-%d' ) -- date_clause
  AND staff_people_id = users.people_id
  AND username =", \$username,
"
ORDER BY
  callback_time DESC
    "]

}
[download]

Now, notice how one line is tagged with the SQL comment:  -- date_clause That is the primary way I wish to mod the SQL, so I cobbled up something to do it:

sub swap_sql {
    my ($sql_fragment, $sub_hint, $sub_expr) = @_;

    $sub_hint = "^.+-- $sub_hint";

    # return data structures as is
    ref $sql_fragment and return $sql_fragment;

    $sql_fragment =~ s/$sub_hint/$sub_expr/m ;
    $sql_fragment;
}
[download]

And then the code to gen sql for tomorrow just requests a line-oriented edit on today's SQL:

sub callbacks_for_tomorrow {

    my $username = shift or confess 'must supply username';

    my $today_sql = callbacks_for_today($username);
    my $tomorrow_date_str = "DATE_FORMAT( `callback_time` , '%Y-%m-%d'
+ ) = DATE_FORMAT( DATE_ADD(NOW( ), INTERVAL 1 DAY) , '%Y-%m-%d' ) -- 
+date_clause";

    my @tomorrow_sql = map (swap_sql($_, 'date_clause', $tomorrow_date
+_str), @$today_sql);

     \@tomorrow_sql;
}
[download]

It would be interesting to see how an ORM would allow for slicing, dicing and decorating a SQL query.

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