Implement sqlite_expand command

[niconoe]

Following discussion with @peterdesmet, it's been decided to create a new command:

$ sqlite_expand db table_name table_schema_path

It takes a sqlite database, a table name and a schema file (example: https://github.com/timrobertson100/frictionless-transforms/blob/master/datasets/periodic_table/transforms/table_schema.json) and:

• add the missing fields to the database
• if possible, change the type of the existing fields
• if possible, reorder fields so working with the database interactively is a bit more friendly

[niconoe]

@peterdesmet: I've done some research about this and it appears that reordering field is not really possible on an existing table. Changing data types/constraints can also be cumbersome. I'm therefore thinking a better way to implement this could be:

• rename the existing table to table_name__old
• create a fresh table table_name based on the schema file (with the right field order, extra constraints, ...)
• copy data from table_name__old to table_name (that might explode in flight if the existing data doesn't fit the field types and constraint defined in the schema). Also warn of data loss if some columns in the original data don't exist in the schema.
• If all if successful, drop table_name__old

Any opinion about this before I jump to implementation? thanks!

[peterdesmet]

That sound reasonable