spec_result_fetch: spec_result_fetch

In r-dbi/DBItest: Testing DBI Backends

spec_result_fetch

Description

spec_result_fetch

Value

dbFetch() always returns a data.frame with as many rows as records were fetched and as many columns as fields in the result set, even if the result is a single value or has one or zero rows. Passing n = NA is supported and returns an arbitrary number of rows (at least one) as specified by the driver, but at most the remaining rows in the result set.

Failure modes

An attempt to fetch from a closed result set raises an error. If the n argument is not an atomic whole number greater or equal to -1 or Inf, an error is raised, but a subsequent call to dbFetch() with proper n argument succeeds.

Calling dbFetch() on a result set from a data manipulation query created by dbSendStatement() can be fetched and return an empty data frame, with a warning.

Specification

Fetching multi-row queries with one or more columns by default returns the entire result. Multi-row queries can also be fetched progressively by passing a whole number (integer or numeric) as the n argument. A value of Inf for the n argument is supported and also returns the full result. If more rows than available are fetched, the result is returned in full without warning. If fewer rows than requested are returned, further fetches will return a data frame with zero rows. If zero rows are fetched, the columns of the data frame are still fully typed. Fetching fewer rows than available is permitted, no warning is issued when clearing the result set.

A column named row_names is treated like any other column.

See Also

Other result specifications: spec_result_clear_result, spec_result_create_table_with_data_type, spec_result_execute, spec_result_get_query, spec_result_roundtrip, spec_result_send_query, spec_result_send_statement

r-dbi/DBItest documentation built on April 15, 2024, 11:26 a.m.