RMySQL (version 0.4-6)

fetch: Fetch records from a previously executed SELECT statement

Description

Fetch records from a previously executed SELECT statement

Usage

fetch(res, n, ...)

Arguments

res

a resultSet object. This object needs to be the result of a SELECT or SELECT-like statement, as produced by dbExec. or dbExecStatement. SQL statements such as INSERT,

n

maximum number of records to retrieve per fetch. Use n = -1 to retrieve all pending records. Some implementations may recognize other special values (RS-MySQL interprets n = 0 to mean "use whatever default was set in the

...

any other database-engine specific arguments.

Value

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

Side Effects

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

Details

See the notes for the various database server implementations.

References

See the Omega Project for Statistical Computing (http://www.omegahat.org) for details on the R/S interface to databases.

See Also

On database managers:

dbManager MySQL load unload

On connections, SQL statements and resultSets:

dbExecStatement dbExec fetch quickSQL

On transaction management:

commit rollback

On meta-data:

describe getVersion getDatabases getTables getFields getCurrentDatabase getTableIndices getException getStatement hasCompleted getRowCount getAffectedRows getNullOk getInfo

Examples

# Run an SQL statement by creating first a resultSet object
> m <- MySQL()
> con <- dbConnect(m)    
> rs <- dbExecStatement(con, 
         statement = "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")
> rs
MySQLResultSet id = (12629,1,3)

# we now fetch the first 100 records from the restulSet into a data.frame
> data1 <- fetch(rs, n = 100)   
> dim(data)
[1] 10  18

> hasCompleted(rs)
[1] 0

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