R中RODBC查询的正确语法是什么

Question

I'm trying to query an Access database using RODBC in R using the code below:

library(RODBC)
channel <- odbcConnectAccess("S:\\mypath\\PhysiPopDONOTTOUCH\\Physiology.mdb")

data <- sqlQuery( channel , paste ("select Endoscopy.*,
Histology.Diagnosis from Endoscopy JOIN PatientData ON
Endoscopy.HospNum_Id=PatientData.HospNum_Id  JOIN Histology ON
Histology.HospNum_Id=PatientData.HospNum_Id WHERE histology.VisitDate
= Endoscopy.VisitDate"))

. This is not successful as I get the error:

[1] "42000 -3506 [Microsoft][ODBC Microsoft Access Driver] Syntax
error in FROM clause."
[2] "[RODBC] ERROR: Could not SQLExecDirect 'select Endoscopy.*,
Histology.Diagnosis from Endoscopy JOIN PatientData ON
Endoscopy.HospNum_Id=PatientData.HospNum_Id  JOIN Histology ON
Histology.HospNum_Id=PatientData.HospNum_Id WHERE Histology.VisitDate
= Endoscopy.VisitDate'"

The tables Endoscopy and Histology are each one to many with the PatientData table. What am I doing wrong with the syntax?

Answer 1

MS Access SQL requires JOIN pairings to be enclosed in parentheses. Also, use of paste() is to eliminate long whitespaces inside string values that appear when you break lines in R. And consider using table aliases to concisely reference tables. Include a semicolon terminator too (see: When should I use semicolons in SQL Server? ). See below adjustment:

data <- sqlQuery(channel , 
                 paste("SELECT e.*, h.Diagnosis",
                       "(FROM PatientData p"
                       "INNER JOIN Endoscopy e p ON e.HospNum_Id = p.HospNum_Id)",
                       "INNER JOIN Histology h ON h.HospNum_Id = p.HospNum_Id",
                       "WHERE h.VisitDate = e.VisitDate;", sep=" "))