The comments below me elaborate a little more clearly, but it's pretty simple. If you have two databases:
DATABASE A
Field List: {Temperature, Price, PART NUMBER, Delivery Time, SERIAL NUMBER}
DATABASE B:
Field List: {Mass, Length, Width, Height, PART NUMBER, Volume, SERIAL NUMBER}
You just have to create a new concatenation of PART NUMBER and SERIAL NUMBER, and now you have a unique identifier that will match between the two databases, and you can easily check which unique instances are present in both databases, and which in A are missing from B and vice versa.
Not sure what your level of coding proficiency is, but a flowchart of how you might get started increasing data wizardry would be something like this:
EXCEL
Master the following functions: INDEX/MATCH, Nested IF statements (especially using AND, OR, XOR, and NOT), IF/ISERROR, ISBLANK, CONCATENATE, and figure out how to combine all of these creatively
Master the creation and formatting of Pivot Tables
POWER QUERY
Master Power Query (you'll want to use online tutorials for this)
Once you're really, really proficient in Power Query, you may as well just start learning SQL and writing your own queries. Udacity and Udemy have multiple excellent free courses in SQL and Python.
Some more keywords you may want to look into:
- Relational Database theory
- Bryce-Codd Normalization
- CRUD applications
- essentialsql.com
- ExcelJet
- MrExcel
- Chandoo
I am by no means a real master, and my degree is in engineering, not programming, but independent research into basic database management has propelled me far past many coworkers in terms of efficacy. It really is astonishing how little the average person knows about proper database operation, despite the fact that most modern companies live and die by the strength of their data.