Here are a few specific suggestions from painful experience:

• As noted, always be mindful of how Perl treats single vs. double quotes.   A literal quote-mark must be escaped with a backslash in a string surrounded by double quotes, but in a string surrounded by single quotes nothing is changed at all.
• Always use query-parameters in your statements.   These are literal (un-quoted) question-marks.   Once you prepare the statement, parameters are substituted when you execute it.   This is not only more efficient for the SQL system, but it also eliminates any threat of “SQL injection,” or simply, “statements that may or may not work, depending on the input data.”   (It will happen to you ... and always at three o’clock in the morning.)
• I suggest retrieving the data using fetchrow_hashref vs. the various other alternatives.   This will return a hashref in which the key is the column-name.   Data::Dumper is also your best friend, because it lets you easily see (while you are writing and then debugging the thing) exactly what the hash-keys will be... whether they are upper or lower or mixed-case or what have you.
• Be mindful of exactly how the various calls return error-conditions.   Make sure that your code actually does test for these errors, and does respond appropriately to them.   (die or croak (mod:://Carp) are very good ways to “hit the ejection-seat” in the middle of complex logic when something unexpectedly goes South.)   Actually test error cases, as well as ones that work properly.