Postgresql placeholders support

[skyien]

Postgres uses "$n" for placeholders.

"The command string can use parameter values, which are referenced in the command as $1 , $2 , etc. These symbols refer to values supplied in the USING clause. This method is often preferable to inserting data values into the command string as text: it avoids run-time overhead of converting the values to text and back, and it is much less prone to SQL-injection attacks since there is no need for quoting or escaping. An example is:"

SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2

https://www.postgresql.org/docs/current/plpgsql-statements.html

[stephencelis]

@skyien Thanks for bringing this up! I've drafted a PR here that starts to decouple things from the ? token format: #78

Let us know if this unblocks you for Postgres support, and please share your progress with us!

[stephencelis]

In the next release you should be able to do:

let (sql, bindings) = query.prepare { "$\($0)" }

[skyien]

Looks great! Thanks, @stephencelis!
I also see that the boolean type is encoded as Int in bindings, but postgres accept boolean only

[stephencelis]

@skyien We recently expanded the binding type to dates and UUIDs and it can/should be further expanded. If you want to PR the change or maintain a branch for Postgres that can eventually be merged, we are definitely down for that.