query shouldn't require mysql/mariadb cli tools

[dd32]

When mysql and mariadb CLI tools are unavailable, wp db query should fallback to using WPDB.

This is particularly important when running with drop-in database engines, and multi-server/partitioned database drivers such as HyperDB.

[swissspidy]

Most of the db commands, including wp db query, also work when WordPress is not installed yet but the database is around, hence the current requirement of the binaries being installed.

We could try falling back to loading WordPress, either implicitly or via an explicit flag such as --load-wordpress that would call Runner::load_wordpress(), so wpdb would be available. Or some custom loading such as we currently do for SQLite in maybe_load_sqlite_dropin(), which loads just a few files.

For HyperDB, see also:

• WordPress database error Unknown column 'Tables_in_' during search-replace search-replace-command#207
• Add support for database sharding ideas#181