fetch

From DBI v0.1-11 by David James

Fetch records from a previously executed query

Fetch records from a previously executed query.

Keywords: interface, database

Usage

fetch(res, n, ...)

Arguments

res: a result set object (one whose class extends DBIResult). This object needs to be the result of a statement that produces output, such as SQL's SELECT or SELECT-like statement, this object res is ty
n: maximum number of records to retrieve per fetch. Use n = -1 to retrieve all pending records. Some implementations may recognize other special values.
...: any other database-engine specific arguments.

Details

See the notes for the various database server implementations.

Value

a data.frame with as many rows as records were fetched and as many columns as fields in the result set.

Note

Make sure you close the result set with dbClearResult as soon as you finish retrieving the records you want.

Side Effects

As the R/Splus client fetches records the remote database server updates its cursor accordingly.

References

See the Database Interface definition document DBI.pdf in the base directory of this package or http://developer.r-project.org/db.

Examples

# Run an SQL statement by creating first a resultSet object
drv <- dbDriver("ODBC")
con <- dbConnect(drv, ...)
res <- dbSendQuery(con, statement = paste(
                      "SELECT w.laser_id, w.wavelength, p.cut_off",
                      "FROM WL w, PURGE P", 
                      "WHERE w.laser_id = p.laser_id",
                      "ORDER BY w.laser_id"))
# we now fetch the first 100 records from the resultSet into a data.frame
data1 <- fetch(res, n = 100)   
dim(data1)

dbHasCompleted(res)

# let's get all remaining records
data2 <- fetch(res, n = -1)

Documentation reproduced from package DBI, version 0.1-11, License: GPL (version 2 or later)

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