backend_dbplyr: Database and SQL generics.

Description

The sql_ generics are used to build the different types of SQL queries. The default implementations in dbplyr generates ANSI 92 compliant SQL. The db_ generics execute actions on the database. The default implementations in dbplyr typically just call the standard DBI S4 method.

Usage

db_desc(x)
sql_translate_env(con)
db_list_tables(con)
db_has_table(con, table)
db_data_type(con, fields)
db_save_query(con, sql, name, temporary = TRUE, ...)
db_begin(con, ...)
db_commit(con, ...)
db_rollback(con, ...)
db_write_table(con, table, types, values, temporary = FALSE, ...)
db_create_table(con, table, types, temporary = FALSE, ...)
db_insert_into(con, table, values, ...)
db_create_indexes(con, table, indexes = NULL, unique = FALSE, ...)
db_create_index(con, table, columns, name = NULL, unique = FALSE, ...)
db_drop_table(con, table, force = FALSE, ...)
db_analyze(con, table, ...)
db_explain(con, sql, ...)
db_query_fields(con, sql, ...)
db_query_rows(con, sql, ...)
sql_select(
  con,
  select,
  from,
  where = NULL,
  group_by = NULL,
  having = NULL,
  order_by = NULL,
  limit = NULL,
  distinct = FALSE,
  ...
)
sql_subquery(con, from, name = random_table_name(), ...)
sql_join(con, x, y, vars, type = "inner", by = NULL, ...)
sql_semi_join(con, x, y, anti = FALSE, by = NULL, ...)
sql_set_op(con, x, y, method)
sql_escape_string(con, x)
sql_escape_ident(con, x)

Value

Usually a logical value indicating success. Most failures should generate an error. However, db_has_table() should return NA if temporary tables cannot be listed with DBI::dbListTables() (due to backend API limitations for example). As a result, you methods will rely on the backend to throw an error if a table exists when it shouldn't.

Arguments

con: A database connection.
table: A string, the table name.
fields: A list of fields, as in a data frame.

Details

A few backend methods do not call the standard DBI S4 methods including

db_data_type(): Calls DBI::dbDataType() for every field (e.g. data frame column) and returns a vector of corresponding SQL data types
db_save_query(): Builds and executes a CREATE [TEMPORARY] TABLE <table> ... SQL command.
db_create_index(): Builds and executes a CREATE INDEX <name> ON <table> SQL command.
db_drop_table(): Builds and executes a DROP TABLE [IF EXISTS] <table> SQL command.
db_analyze(): Builds and executes an ANALYZE <table> SQL command.

Currently, copy_to() is the only user of db_begin(), db_commit(), db_rollback(), db_write_table(), db_create_indexes(), db_drop_table() and db_analyze(). If you find yourself overriding many of these functions it may suggest that you should just override copy_to() instead.

db_create_table() and db_insert_into() have been deprecated in favour of db_write_table().