RODBC (version 1.0-2)

sqlQuery: Query an ODBC Database

Description

Submit an SQL query to an ODBC database, and retrieve the results.

Usage

sqlQuery(channel, query, errors = TRUE, ...)
sqlGetResults(channel, as.is = FALSE,  errors = FALSE,
              max = 0, buffsize = 1000,
              nullstring = NA, na.strings = "NA",
              believeNRows = TRUE, dec = getOption("dec"))

Arguments

channel

connection handle as returned by odbcConnect.

query

any valid SQL statement

errors

if TRUE halt and display error, else return -1

...

additional arguments to be passed to sqlGetResults.

as.is

which (if any) character columns should be converted, as in read.table? See the details.

max

limit on the number of rows to fetch, with 0 indicating no limit.

buffsize

the number of rows to be transferred at a time.

nullstring

character string to be used when reading SQL_NULL_DATA character items from the database.

na.strings

character string(s) to be mapped to NA when reading character data.

believeNRows

logical. Is the number of rows returned by the ODBC connection believable? This might already be set to false when the channel was opened, and can that setting cannot be overriden.

dec

The character for the decimal place to be assumed when converting character columns.

Value

• A data frame (possibly with 0 rows) on success. If errors = TRUE, a character vector of error message(s), otherwise error code -1 (general, call odbcGetErrMsg for details) or -2 (no data, which may not be an error as some SQL commands do return no data).

Details

sqlQuery is the workhorse function of RODBC. It sends the SQL statement query to the server, using connection channel returned by odbcConnect.

SQL beginners should note that the term `Query' includes any valid SQL statement including table creation, alteration, updates etc as well as SELECTs. The sqlQuery command is a convenience wrapper that calls first odbcQuery and then sqlGetResults. If finer-grained control is needed, for example over the number of rows fetched, these functions should be called directly or additional arguments passed to sqlQuery.

sqlGetResults is a mid-level function. It should be called after a call to odbcQuery and used to retrieve waiting results into a dataframe. Its main use is with max set to non zero it will retrieve the result set in batches with repeated calls. This is useful for very large result sets which can be subjected to intermediate processing. It makes use of the setting of options("dec") to determine the character used in setting decimal points. This is set to "." when RODBC is initialized if it is not already set.

Where possible sqlGetResults transfers data directly: this happens for double, real, integer and smallint columns in the table. All other SQL data types are converted to character strings (of length up to 256), and then converted by type.convert as controlled by the as.is argument. Note that almost all callers set as.is = TRUE. Using buffsize will yield a marginal increase in speed if set to more than the maximum number of rows where believeNRows = FALSE.

See Also

odbcConnect, sqlFetch, sqlSave, sqlTables, odbcQuery

Examples

library(RODBC)
data(USArrests)
channel <- odbcConnect("test", "", "") # userId and password
sqlSave(channel, USArrests, rownames = "State", verbose = TRUE)
options(dec=".") # this is the default decimal point
## note case of State, Murder, rape are DBMS-dependent.
sqlQuery(channel, "select State, Murder from USArrests where rape > 30 order by Murder")
odbcClose(channel)