Fetch records from a previously executed query.

Description

Fetch the next n elements (rows) from the result set and return them as a data.frame.

Usage

dbFetch(res, n = -1, ...)

fetch(res, n = -1, ...)

Arguments

Details

fetch is provided for compatibility with older DBI clients - for all new code you are strongly encouraged to use dbFetch. The default method for dbFetch calls fetch so that it is compatible with existing code. Implementors should provide methods for both fetch and dbFetch until fetch is deprecated in 2015.

Value

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

See Also

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

Other DBIResult generics: dbClearResult, dbColumnInfo, dbGetRowCount, dbGetRowsAffected, dbGetStatement, dbHasCompleted

Examples

if (!require("RSQLite")) {
con <- dbConnect(RSQLite::SQLite(), ":memory:")
dbWriteTable(con, "mtcars", mtcars)

# Fetch all results
res <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
dbFetch(res)
dbClearResult(res)

# Fetch in chunks
res <- dbSendQuery(con, "SELECT * FROM mtcars")
while (!dbHasCompleted(res)) {
  chunk <- fetch(res, 10)
  print(nrow(chunk))
}
dbClearResult(res)
dbDisconnect(con)
}

Results

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

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> library(DBI)
> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/DBI/dbFetch.Rd_%03d_medium.png", width=480, height=480)
> ### Name: dbFetch
> ### Title: Fetch records from a previously executed query.
> ### Aliases: dbFetch dbFetch,DBIResult-method fetch
> 
> ### ** Examples
> 
> if (!require("RSQLite")) {
+ con <- dbConnect(RSQLite::SQLite(), ":memory:")
+ dbWriteTable(con, "mtcars", mtcars)
+ 
+ # Fetch all results
+ res <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
+ dbFetch(res)
+ dbClearResult(res)
+ 
+ # Fetch in chunks
+ res <- dbSendQuery(con, "SELECT * FROM mtcars")
+ while (!dbHasCompleted(res)) {
+   chunk <- fetch(res, 10)
+   print(nrow(chunk))
+ }
+ dbClearResult(res)
+ dbDisconnect(con)
+ }
Loading required package: RSQLite
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>