As an experienced PHP developer, I possess a rock-solid mastery over the database technologies such as MySQL and SQL queries. With my strong understanding of data manipulation among multiple tables and excellent problem-solving abilities, your MySQL script for multi-table sum calculation is well within my wheelhouse. The complexities of filtering items based on date range and specific field values are not new to me; in fact, they're challenges that I find stimulating!
Moreover, I fully comprehend the importance of effective communication while working on a project of this nature, where a deep understanding of the complex database structure will be crucial. I assure you of my unwavering dedication to unravelling your data hierarchy, designing an appropriate script solution and delivering results that match your high standards.
In a nutshell, you can place your full trust in my skills, proficiency and experience with PHP and SQL queries to tackle your project head-on. I’m excited at the prospect of solving complex puzzles like yours, and look forward to potentially collaborating with you on this task. Give me this opportunity to showcase my skills,and you won't be disappointed!