Merge 4 databases and migrate to WordPress

Transfer of the largest economic media Global Economic Intersection with preservation of 11-year history (more than 120,000 posts).

It is necessary to combine data from several unrelated databases into one database managed by WordPress.

The client needed a database that would include posts from several other databases.
It was required to save:

1) Headings and content of articles;
2) Meta title and description;
3) The structure of links.

The combined data should work with WordPress.

Data sources:

1) 2 bases b2evolution – 27000 posts.
2) WordPress database – 49000 posts
3) 45,000 posts like HTML-pages without a database.

Solving the problem:

1) To collect data from b2evolution, you need to link 3 tables: content table, authors table, categories table. A table consisting of data for further import is formed through MySQL queries.
2) The main difficulty when transferring is a large SQL table. I used the utility to work with big data.
3) The client did not know about these posts. I managed to find about 45,000 records.
To combine them into one file for import, I wrote a parser script that collected data into several text files.

Difficulties and solutions:

– each database contained a link structure not typical for WordPress. I used redirects, regular expressions, and the Permalink Manager plugin.