如何对我在Wordpress数据库中创建的自定义表进行sql注入证明调用?

So here is what im trying to accomplish: I have worked with SQL plenty of times in the past, but it was always with coldfusion, never with PHP. I have looked over the syntax for making sql queries and have come up with this much (i do believe that using prepare helps protect against sql-injection). My overall goal is to have a page set up to where it pulls all the rows from the jewelry table that has the cat_id corresponding with the categories table. Im just not sure if im starting this off correctly or not. The jewelry table has 4 fields (id, cat id, name, and image)So here is what im trying to accomplish: I have