MySQL {RMySQL}R Documentation

Instantiate a MySQL client from the current R or S-Plus session

Description

This function creates and initializes a MySQL client. It returns an driver object that allows you to connect to one or several MySQL servers.

Usage

MySQL(max.con = 10, fetch.default.rec = 500, force.reload = F)

Arguments

max.con maximum number of connections that we intended to have open. This can be up to 100, a limit defined at compilation time. Strictly speaking this limit applies to MySQL servers, but clients can have (at least in theory) more than this.
fetch.default.rec number of records to fetch at one time from the database. (The fetch method uses this number as a default.)
force.reload should we reload (reinitialize) the client code? Setting this to TRUE allows you to change default settings. Notice that all connections should be closed before re-loading.

Details

This object is a singleton, that is, on subsequent invocations it returns the same initialized object.

This implementation allows you to connect to multiple host servers and run multiple connections on each server simultaneously.

Value

An object MySQLDriver that extends dbDriver and dbObjectId. This object is required to create connections to one or several MySQL database engines.

Side Effects

The R/S-Plus client part of the database communication is initialized, but note that connecting to the database engine needs to be done through calls to dbConnect.

User authentication

The preferred method to pass authentication parameters to the server (e.g., user, password, host) is through the MySQL personal configuration file `$HOME/.my.cnf' (or `c:/my.cnf' under Windows). Since specifying passwords on calls to dbConnect is a very bad idea (and so is specifying passwords through shell variables), the client code parses the configuration file `$HOME/.my.cnf'; this file consists of zero or more sections, each starting with a line of the form [section-name], for instance

$ cat $HOME/.my.cnf
# this is a comment
[client]
user = dj
host = localhost

[rs-dbi]
database = s-data

[lasers]
user = opto
database = opto
password = pure-light
host = merced
...
[iptraffic]
host = data
database = iptraffic

This file should be readeable only by you. Inside each section, MySQL parameters may be specified one per line (e.g., user = opto). The R/S MySQL implementation always parses the [client] and [rs-dbi] sections, but you may define you own project-specific sections to tailor its environment; if the same parameter appears more than once, the last (closer to the bottom) occurrence is used.

If you define a section, say, [iptraffic], then instead of including all these parameters in the call to dbConnect, you simply supply the name of the group, e.g., dbConnect(mgr, group = "iptraffic").

The most important parameters are user, password, host, and dbname.

References

See the Omega Project for Statistical Computing at http://www.omegahat.org for more details on the R/S database interface.

See the documentation at the MySQL Web site http://www.mysql.com for details.

Author(s)

David A. James

See Also

On database managers:

dbDriver dbUnloadDriver

On connections, SQL statements and resultSets:

dbConnect dbDisconnect dbSendQuery dbGetQuery fetch dbClearResult

On transaction management:

dbCommit dbRollback

On meta-data:

summary dbGetInfo dbGetDBIVersion dbListTables dbListConnections dbListResults dbColumnInfo dbGetException dbGetStatement dbHasCompleted dbGetRowCount dbGetAffectedRows

Examples

# create a MySQL instance and create one connection.
> m <- dbDriver("MySQL")
<MySQLDriver:(4378)>

# open the connection using user, passsword, etc., as
# specified in the "[iptraffic]" section of the 
# configuration file \file{\$HOME/.my.cnf}
> con <- dbConnect(m, group = "iptraffic")
> rs <- dbSendQuery(con, "select * from HTTP_ACCESS where IP_ADDRESS = '127.0.0.1'")
> df <- fetch(rs, n = 50)
> dbHasCompleted(rs)
[1] FALSE
> df2 <- fetch(rs, n = -1)
> dbHasCompleted(rs)
[1] TRUE
> dbClearResult(rs)
> dim(dbGetQuery(con, "show tables"))
[1] 74   1
> dbListTables(con)    


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