gmRead: Return the result of an SQl query given as R-like representation

Description

gmRead translates the R representation expr of an SQL query into SQL and evaluates it in the database db.

Usage

gmRead(expr,envir=parent.frame(),EXPR=substitute(expr),limit=-1,db=getOption("gmDB"))
gmReadInternal(EXPR,sel=NULL,db,gmNameVarID=getGmNameVarID(db))

Arguments

expr

R expression of an SQL query. Expressions created with gmExpr can be used as well.

envir

defines the environment used for evaluation of expr.

EXPR

The quoted version of such an expression.

sel

The selection statement in R representation.

limit

defines the number of lines returned in the query.

defines the database, on which the query will be run.

gmNameVarID

The gmVarID in the gmDatabase of gmName for later referencing of an object by its name in the gmDatabase.

Value

For gmRead a dataframe is returned. It contains the requested data. For gmReadInternal a call is returned, consisting of an expression to be interpreted as the R representation of SQL by gmSQL. Furthermore a list of the asked variables in EXPR and the columns, where to look in the database tables are returned, too.

Details

gmRead is the principal function of the gmDatabase package. It provides the main functionality: Receiving an R expression expr of an SQL query, it returns a dataframe, containing the requested data. On the other hand, gmReadInternal, indicated by its notation, is meant for in-package use only. During the execution of gmRead it creates a call containing the R representation, which is used later in gmSQL to create and run a proper SQL query against the database.

Examples

Run this code

## Not run: 
# .gmDB <- dbConnect(...)
# root <- "root"
# erg <- gmRead(root)
# ## returns the ID of root in the database
# 
# gmRead(root$project[gmTitle=group])
# ## groups
# ## End(Not run)