copy_dm_to(copy_to = ) is defunct

[krlmlr]

without a really good alternative.

[krlmlr]

copy_dm_to() currently:

• collects the dm
• creates the SQL for the tables and indexes
• executes the SQL to create the tables
• populates the tables
• executes the SQL to create the indexes
• creates a dm with the new remote tables replacing the original tables in the dm, and the structure unchanged

Can we create a nice user-facing API for each of these items? Ideally, with customization options as suggested in #1388?

[krlmlr]

Naming is hardest.

• sql_dm_create() for creating the SQL
• map(queries, dbExecute) can be done by the user? Or provide a lightweight helper that can optionally wrap in a transaction?
• populating could be done with dm_rows_append() by default if we allow copy = TRUE (and then there should be specialized handling for copy = TRUE in dbplyr)
• for combining new tables with the existing structure of a dm we need a better dm_paste() (I thought I had filed an issue but apparently haven't, perhaps dm_paste() for database tables #1174 is vaguely related)