WP-CLI is a great tool for migrating data within WordPress from the command line, however it’s not always the appropriate or most efficient way to move data around. My rule of thumb is if I am working with unserialized data, I try to use MySQL queries first.
A simple migration script with WP-CLI could take up a lot of I/O and could take minutes or hours to complete depending on the data set. The same query in MySQL can take mere seconds. For example, if you wanted to take meta values from a specific post type, and move them to a new key, the WP-CLI script might look something like this: