db.Rquery-class: Class '"db.Rquery"' and its sub-class 'db.Rview-class'

In greenplum-db/GreenplumR: A Fast, Easy-to-Use Tool for Manipulating Tables in Databases

Class "db.Rquery" and its sub-class db.Rview-class

Description

An object of this class represents a series of operations applied onto an existing db.data.frame object. These operations are actually a SQL query, which one can choose to materialize in the database using as.db.data.frame. lk can fetch a part of the result of executing the SQL query. Thus one does not need to create a table for every step of the operations, and the data transfered between R and the database is minimized.

Objects from the Class

Objects can be created by almost all functions/methods that can be applied onto db.data.frame except content, lk and delete.

db.Rview-class is a sub-class of db.Rquery-class, and it behaves just like "view" in the databases except that it exists only in R. Usually there is no difference to use db.Rview or db.Rquery. as.db.Rview casts a db.Rquery object into a db.Rview object.

Usually it is NOT recommended to directly manipulate the internal slots of these objects.

Slots

.content:

Object of class "character". The SQL query that represents the operations. The function content can get this value.

.expr:

Object of class "character". An array of expression strings for columns of the table that the SQL query can be materialized into. It is not to used by the normal users.

.source:

Object of class "character". A string, the table/view name which this SQL query is originated. It is not to used by the normal users.

.parent:

Object of class "character". A string. In the SQl query it is the part after "from". It is not to used by the normal users.

.conn.id:

Object of class "numeric", an integer. The ID number of the database connection where .source resides. The functions conn.id and conn.id<- can get and set this value.

.col.name:

Object of class "character". An array of strings. The names of columns of the table that the SQL query can be materialized into. The S4 method names,db.obj-method gets this value.

.key:

Object of class "character". The name of the primary key column name in .source. Currently only one primary key column is supported. This value can be set during the creation of the object when using the function db.data.frame. The functions key and key<- can be used to get and set this value.

.col.data_type:

Object of class "character". The 1D array of column data types of the table that the SQL query can be materialized into. This is not supposed to be used by the normal user.

.col.udt_name:

Object of class "character". The 1D array of column udt names of the table that the SQL query can be materialized into. This is not to used by normal users.

.where:

Object of class "character". The condition string used in "where" inside the SQL query.

.is.factor:

Object of class "logical". An array of logical values which indicate whether each column of the table that the SQL query can be materialized into is a factor. This is not to be used by the normal users.

.factor.suffix:

Object of class "character". An array of strings for every column. When creating dummy columns for a factor column, we add a random string in the names of the dummy columns to avoid naming conflicts. So a factor column's .factor.suffix is a random string, otherwise it is just an empty string. This is not to be used by the normal users.

.factor.ref:

The value of the factor reference level for the regressions. If it is NA, then the regressions automatically select a reference level.

.sort:

Object of class "list". The list contains the information used for "order by" in the SQL query.

by: A string. The column names that are used in "order by".

order: A string, "" or "desc"

str: A string, the full "order by ..." string.

.is.agg:

logical value, whether this object represents an aggregate operation.

.dist.by:

A string, the distribution policy for the original data table, which is used to construct this db.Rquery object, when using Greenplum database or HAWQ. It can be character(0), which means the original data table is distributed randomly. Or it can be a string of column names separated by comma, which are the columns that are used in the "distributed by" when the original table was created.

Extends

Class "db.obj", directly.

Methods

All methods for db.data.frame can be applied onto this class.

Author(s)

Author: Predictive Analytics Team at Pivotal Inc.

Maintainer: Frank McQuillan, Pivotal Inc. [e-mail]

See Also

db.data.frame creates a db.data.frame object.

as.db.data.frame converts db.Rquery object, data.frame, or a data file into a db.data.frame object and at the same time creates a new table in the database.

as.db.Rview converts a db.Rquery object to a db.Rview object.

db.obj is the superclass.

Class db.data.frame is another sub-class of db.obj.

lk display a part of the table

Examples

## Not run: 
showClass("db.Rquery")



## set up the database connection
## Assume that .port is port number and .dbname is the database name
cid <- db.connect(port = .port, dbname = .dbname)

delete("abalone", conn.id = cid)
x <- as.db.data.frame(abalone, "abalone", conn.id = cid)

## create several db.Rquery objects
y <- x[,1:2]
z <- x[x$rings > 10,]

dim(z) # get an error

lk(y)

lk(z)

## materialize a db.Rquery object
z <- as.db.data.frame(z, "abalone_rings_larger_10")
delete("abalone_rings_larger_10", conn.id = cid)

dim(z) # no error

db.disconnect(cid, verbose = FALSE)

## End(Not run)

greenplum-db/GreenplumR documentation built on Sept. 2, 2023, 8:09 a.m.