Investigate whether temp tables should be supported

[imanuelcostigan]

In particular, within db_list_tables and db_has_table. It may be necessary because tbl_sql and copy_to check for the existence of a table.

NB: temp table support was removed in 7679476 because JDBC API does not support this.

[imanuelcostigan]

Recent MSFT documentation of temp tables here

[imanuelcostigan]

Alternative is to follow db_has_table() method for MySQL:

db_has_table.MySQLConnection <- function(con, table, ...) {
  # MySQL has no way to list temporary tables, so we always NA to
  # skip any local checks and rely on the database to throw informative errors
  NA
}