Add support for primary keys in dbCreateTable() and sqlCreateTable()

[krlmlr]

This is important, because it is difficult and computationally intensive (and sometimes impossible) to change the primary key after creating the table.

Should we also support foreign keys and unique constraints?

This is a blocker for cynkra/dm#3. We would also need to adapt dbplyr::copy_to() and perhaps dbplyr::compute().

[hadley]

How standard is this syntax?

[krlmlr]

Pretty much, I think, but I don't know. We'll find out soon enough, we can override in backends -- this is a method.

[hadley]

This seems too short compared to other argument names

[krlmlr]

primary.key? I'm not sure this package already uses underscores for argument names :-\

[pnacht]

As I understand it, DBI tries to be SQL 99 compliant. If so, I believe the standard syntax is in fact

CREATE TABLE {tableName} (
	{column Definitions}, 
	CONSTRAINT {PK_Name} PRIMARY KEY ({column Names}) 
) 

Per W3Schools, the PRIMARY KEY (x) syntax is only valid for MySQL.

[vnijs]

I was looking for a way to add a primary key when using dbCreateTable() or dbWriteTable(). Specifically, updating a row if a key is present or adding a row if not, using the below requires a constraint or primary key. Is there still a plan to add the option in this PR? Would be very convenient. Thanks

upsert_str <- glue::glue("INSERT INTO student_data ({vars_str}) VALUES ({values_str}) ON CONFLICT({key_str}) DO UPDATE SET {set_str}")
dbExecute(pool, upsert_str)

[krlmlr]

@vnijs: The dm package supports this via copy_dm_to(set_key_constraints = TRUE) : https://cynkra.github.io/dm/articles/howto-dm-copy.html#copy-model. The documentation doesn't mention this explicitly, it should.

[vnijs]

@krlmlr dm looks like an excellent package! Thanks for the reference. The below worked, where db is the connection made using DBI.

dm_sdata <- dm(pre_student_data = pre_sdata, student_data = sdata) %>%
  dm_add_pk(pre_student_data, user_name) %>%
  dm_add_pk(student_data, user_name)

## create sqlite dbase in site directory
copy_dm_to(db, dm_sdata, temporary = FALSE)