Typically, each instance of WordPress has it’s own database. If you have 20+ seperate WordPress installs, then you should have 20+ different databases. Each database is going to have quite a few tables.
If it is asking you to clear the database tables, then it is most likely only referring to the data for a single WordPress install: namely, the one your are installing Multisite on. In other words, your 20+ other WordPress installations should be safe.
However, when installing Multisite, it is always a good idea to back up your databases.
As far as using it to manage your sites, I’m not sure if multisite is the best solution. There are plenty of plugins that will perform the function you need, without having to manipulate databases.
Related Posts:
- Moving a WP Multisite to a subdirectory
- Multisite in subfolder – How to make new sites to be in same level subfolders as the main site
- How to individually set WP_DEBUG on a sub-directory multisite?
- Benefits or Problems for using Sub-Directory vs Sub-Domain install of WP Network
- Multisite: differences between subdomain and subdirectory mode? Can it be switch after installation?
- NGinx + WordPress Subdomain Multi with core in Subdirectory
- Multisite installation combining subdomains and subdirectories
- Suppress subdirectory from WordPress Multisite primary URL
- Subfolder multisite issue. Themes and plugin files 404
- How to do Domain Mapping to Subdirectories?
- Limit multisite/network site names to a property of the user
- On WordPress Network(multisite), Sub Blogs in Subdirectories or Subdomains? What’s better?
- Change multi-site installation from sub-domains to sub-directories
- Subdirectory multisite installation with several domain names?
- Can’t access WordPress multisite after connecting to domain
- WordPress multisite subdirectory on nginx behind reverse proxy
- Media library not loading after switching the main site of multisite
- Depth > 2 possible with multisite?
- How to run a subdirectory multisite install under a subdomain
- Make a user administrator to a sub directory site and a contributor to main site in multisite network
- Multisite setup help – plain domain/subsite always redirects to domain with subdir multisite
- Multiple wordpress installations that shares WordPress & Theme but with separated database
- WordPress Multisite new sites in directory
- multisite subdomain behind reverse proxy
- Multisite Subdirectory with same domain subdomain
- How to host unrelated pages on WordPress domain
- One Domain, Two Installs of WordPress
- Multisite installation on an existing single installation
- why there is a large file named core in wpmu’s directory?
- Multisite – One Site with multiple URLs
- Sub-sub folders of WordPress Multisite subdirectory
- How to organize my js files
- After setting up multisite on localhost, requests to localhost redirect to production domain
- Working with Reverse Proxies and Multisite Installation
- Can I use the same Folder name as a Multisite Blog?
- Multisite for main in subdirectory, subdomain and subfolders (EN/ES)
- Infamous admin login redirect
- Trying to Decide Between Reverse-proxy and Multisite
- How to use the same “wp_posts” table for different subdirectories in the same DB?
- multisite installed on subdomain now want another subsite on subdirectory
- Structure of multilingual and multiregional directory listing website for translation
- Problems with WordPress multisite directories/url structures and admin access after migration
- Using WordPress multisite for subsites only
- How do I split a single WPML site with 6 languages (English is Main) into Multisite with 5 subfolders
- Sub-directory domain on subdomain multisite?
- Using multisite, how can I get two different sites on the network to have different active themes?
- Max number of sub folders
- Multisites with different root directory
- WordPress Multisite subdomains and sharing the same upload folder
- WordPress Multisite with thousands of blog
- Nested folder paths for WordPress multisite
- WordPress Multisite redirect loop
- Multisite, different domains, optional subdirectory, and htaccess
- Subdirectory and domain multisite installation
- Installed in root, want second in subdirectory
- WP Multisite .htaccess interferes with cgi-bin
- Multisite installation without using domain root
- Primary site file uploads failing, subdirectory subsites upload fine
- How to put a Custom Folder under one sub-site of Multisite WP?
- How can I set up a completely separate (not multisite) WordPress installation as a subdirectory of an existing WordPress blog?
- How do I make a copy of WordPress to other folder
- Is it possible to install a different wordpress installation in a subdirectory? [duplicate]
- Moved WP Multisite, cannot access sites
- Multi site root site installed on subdomain, with child sites as subdirectories
- WordPress multisite with subdomains behind nginx reverse proxy using subdirectories
- Best way to set up multiple urls for the same WordPress site?
- WordPress: How to change name of ADD-ON domain’s folder and also change/rename all references to it
- Upload path/URL weirdness for the main blog of a multisite/network setup
- WP_Site_Query vs. WP_Network_Query in WordPress 4.6
- Multisite/network–automatic self-registration, blog setup
- Restrict users on multisite WordPress install
- Using separate Apache log files for multisite
- Network setup tab is not shown under Tools
- How can I get multisite primary blog (url or path) for current user?
- Yoast Sitemap grouping external sitemaps [closed]
- How to allow WordPress users create sub-website or mini-website under my domain with any basic site builder?
- Stop WordPress Entirely and Run My Own Code
- What is meant by Multisite in WordPress?
- Allow Author on Site A capability to upload files on Site B in Multi Site
- WordPress Network (multisite) — how to ensure each site has their own admin URL?
- Is it possible for a child-site of a multisite to be a multisite itself?
- Migrating static site to multisite with multiple domains and subdomains
- Share DB tables between two blogs on the same WP Multisite installation
- 404 redirecting to home [closed]
- How do I check if the user is a site owner in a network?
- get_user_meta() in multiste with respect to subdomain
- Different Domains in Multisite Setup
- Using wp_insert_post with WP Network in a cron script
- featured image metabox MU
- wp cli search and replace on –network Error reconnecting to the database
- Multisites can’t load .php files
- How to set upload path after renaming uploads folder in Multisite?
- WordPress Multisite FQDN Admin Access
- Multisite subdirectory root not accessible
- Should I use individual WordPress installs or WordPress-Mutisite install?
- How do I combine wp_redirect and add_filter?
- Pointing multiple subdomains at the same WordPress Installation
- Multisite redirect loop for a single www domain
- Multisite subdirectory blogs missing slash
- wordpress multisite is broken in nginx but working in apache